Template Class basic_json

• Defined in File json.hpp

Nested Relationships

Nested Types

• Union basic_json::json_value

Class Documentation

template<template<typename U, typename V, typename ...Args> class ObjectType = std::map, template<typename U, typename ...Args> class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template<typename U> class AllocatorType = std::allocator, template<typename T, typename SFINAE = void> class JSONSerializer = adl_serializer>
class basic_json

a class to store JSON values

@requirement The class satisfies the following concept requirements:

• Basic

  • DefaultConstructible: JSON values can be default constructed. The result will be a JSON null value.

  • MoveConstructible: A JSON value can be constructed from an rvalue argument.

  • CopyConstructible: A JSON value can be copy-constructed from an lvalue expression.

  • MoveAssignable: A JSON value van be assigned from an rvalue argument.

  • CopyAssignable: A JSON value can be copy-assigned from an lvalue expression.

  • Destructible: JSON values can be destructed.

• Layout

  • StandardLayoutType: JSON values have standard layout: All non-static data members are private and standard layout types, the class has no virtual functions or (virtual) base classes.

• Library-wide

  • EqualityComparable: JSON values can be compared with ==, see operator==(const_reference,const_reference).

  • LessThanComparable: JSON values can be compared with <, see operator<(const_reference,const_reference).

  • Swappable: Any JSON lvalue or rvalue of can be swapped with any lvalue or rvalue of other compatible types, using unqualified function call swap().

  • NullablePointer: JSON values can be compared against std::nullptr_t objects which are used to model the null value.

• Container

  • Container: JSON values can be used like STL containers and provide iterator access.

  • ReversibleContainer; JSON values can be used like STL containers and provide reverse iterator access.

@requirement The class satisfies the following concept requirements:

• Basic

  • DefaultConstructible: JSON values can be default constructed. The result will be a JSON null value.

  • MoveConstructible: A JSON value can be constructed from an rvalue argument.

  • CopyConstructible: A JSON value can be copy-constructed from an lvalue expression.

  • MoveAssignable: A JSON value van be assigned from an rvalue argument.

  • CopyAssignable: A JSON value can be copy-assigned from an lvalue expression.

  • Destructible: JSON values can be destructed.

• Layout

  • StandardLayoutType: JSON values have standard layout: All non-static data members are private and standard layout types, the class has no virtual functions or (virtual) base classes.

• Library-wide

  • EqualityComparable: JSON values can be compared with ==, see operator==(const_reference,const_reference).

  • LessThanComparable: JSON values can be compared with <, see operator<(const_reference,const_reference).

  • Swappable: Any JSON lvalue or rvalue of can be swapped with any lvalue or rvalue of other compatible types, using unqualified function call swap().

  • NullablePointer: JSON values can be compared against std::nullptr_t objects which are used to model the null value.

• Container

  • Container: JSON values can be used like STL containers and provide iterator access.

  • ReversibleContainer; JSON values can be used like STL containers and provide reverse iterator access.

See also

RFC 7159: The JavaScript Object Notation (JSON) Data Interchange Format

Invariant

The member variables m_value and m_type have the following relationship:

• If m_type == value_t::object, then m_value.object != nullptr.

• If m_type == value_t::array, then m_value.array != nullptr.

• If m_type == value_t::string, then m_value.string != nullptr. The invariants are checked by member function assert_invariant().

Since

version 1.0.0

See also

RFC 7159: The JavaScript Object Notation (JSON) Data Interchange Format

Invariant

The member variables m_value and m_type have the following relationship:

• If m_type == value_t::object, then m_value.object != nullptr.

• If m_type == value_t::array, then m_value.array != nullptr.

• If m_type == value_t::string, then m_value.string != nullptr. The invariants are checked by member function assert_invariant().

Since

version 1.0.0

Template Parameters:

• ObjectType – type for JSON objects (std::map by default; will be used in object_t)

• ArrayType – type for JSON arrays (std::vector by default; will be used in array_t)

• StringType – type for JSON strings and object keys (std::string by default; will be used in string_t)

• BooleanType – type for JSON booleans (bool by default; will be used in boolean_t)

• NumberIntegerType – type for JSON integer numbers (int64_t by default; will be used in number_integer_t)

• NumberUnsignedType – type for JSON unsigned integer numbers ( by default; will be used in number_unsigned_t)

• NumberFloatType – type for JSON floating-point numbers (double by default; will be used in number_float_t)

• AllocatorType – type of the allocator to use (std::allocator by default)

• JSONSerializer – the serializer to resolve internal calls to to_json() and from_json() (adl_serializer by default)

• ObjectType – type for JSON objects (std::map by default; will be used in object_t)

• ArrayType – type for JSON arrays (std::vector by default; will be used in array_t)

• StringType – type for JSON strings and object keys (std::string by default; will be used in string_t)

• BooleanType – type for JSON booleans (bool by default; will be used in boolean_t)

• NumberIntegerType – type for JSON integer numbers (int64_t by default; will be used in number_integer_t)

• NumberUnsignedType – type for JSON unsigned integer numbers ( by default; will be used in number_unsigned_t)

• NumberFloatType – type for JSON floating-point numbers (double by default; will be used in number_float_t)

• BinaryType – type for packed binary data for compatibility with binary serialization formats (std::vector<std::uint8_t> by default; will be used in binary_t)

• AllocatorType – type of the allocator to use (std::allocator by default)

• JSONSerializer – the serializer to resolve internal calls to to_json() and from_json() (adl_serializer by default)

exceptions

Classes to implement user-defined exceptions.

using exception = detail::exception

general exception of the basic_json class

This class is an extension of std::exception objects with a member id for exception ids. It is used as the base class for all exceptions thrown by the basic_json class. This class can hence be used as “wildcard” to catch exceptions.

Subclasses:

• parse_error for exceptions indicating a parse error

• invalid_iterator for exceptions indicating errors with iterators

• type_error for exceptions indicating executing a member function with a wrong type

• out_of_range for exceptions indicating access out of the defined range

• other_error for exceptions indicating other library errors

@liveexample{The following code shows how arbitrary library exceptions can be caught.,exception}

Since

version 3.0.0

using parse_error = detail::parse_error

exception indicating a parse error

This exception is thrown by the library when a parse error occurs. Parse errors can occur during the deserialization of JSON text, CBOR, MessagePack, as well as when using JSON Patch.

Member byte holds the byte index of the last read character in the input file.

Exceptions have ids 1xx.

name / id	example message	description
json.exception.parse_error.101	parse error at 2: unexpected end of input; expected string literal	This error indicates a syntax error while deserializing a JSON text. The error message describes that an unexpected token (character) was encountered, and the member byte indicates the error position.
json.exception.parse_error.102	parse error at 14: missing or wrong low surrogate	JSON uses the \uxxxx format to describe Unicode characters. Code points above above 0xFFFF are split into two \uxxxx entries (“surrogate pairs”). This error indicates that the surrogate pair is incomplete or contains an invalid code point.
json.exception.parse_error.103	parse error: code points above 0x10FFFF are invalid	Unicode supports code points up to 0x10FFFF. Code points above 0x10FFFF are invalid.
json.exception.parse_error.104	parse error: JSON patch must be an array of objects	RFC 6902 requires a JSON Patch document to be a JSON document that represents an array of objects.
json.exception.parse_error.105	parse error: operation must have string member ‘op’	An operation of a JSON Patch document must contain exactly one “op” member, whose value indicates the operation to perform. Its value must be one of “add”, “remove”, “replace”, “move”, “copy”, or “test”; other values are errors.
json.exception.parse_error.106	parse error: array index ‘01’ must not begin with ‘0’	An array index in a JSON Pointer (RFC 6901) may be 0 or any number without a leading 0.
json.exception.parse_error.107	parse error: JSON pointer must be empty or begin with ‘/’ - was: ‘foo’	A JSON Pointer must be a Unicode string containing a sequence of zero or more reference tokens, each prefixed by a / character.
json.exception.parse_error.108	parse error: escape character ‘~’ must be followed with ‘0’ or ‘1’	In a JSON Pointer, only ~0 and ~1 are valid escape sequences.
json.exception.parse_error.109	parse error: array index ‘one’ is not a number	A JSON Pointer array index must be a number.
json.exception.parse_error.110	parse error at 1: cannot read 2 bytes from vector	When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
json.exception.parse_error.112	parse error at 1: error reading CBOR; last byte: 0xF8	Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
json.exception.parse_error.113	parse error at 2: expected a CBOR string; last byte: 0x98	While parsing a map key, a value that is not a string has been read.
json.exception.parse_error.114	parse error: Unsupported BSON record type 0x0F	The parsing of the corresponding BSON record type is not implemented (yet).

@liveexample{The following code shows how a parse_error exception can be caught.,parse_error}

This exception is thrown by the library when a parse error occurs. Parse errors can occur during the deserialization of JSON text, CBOR, MessagePack, as well as when using JSON Patch.

See also

- exception for the base class of the library exceptions

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

Member byte holds the byte index of the last read character in the input file.

Exceptions have ids 1xx.

name / id	example message	description
json.exception.parse_error.101	parse error at 2: unexpected end of input; expected string literal	This error indicates a syntax error while deserializing a JSON text. The error message describes that an unexpected token (character) was encountered, and the member byte indicates the error position.
json.exception.parse_error.102	parse error at 14: missing or wrong low surrogate	JSON uses the \uxxxx format to describe Unicode characters. Code points above above 0xFFFF are split into two \uxxxx entries (“surrogate pairs”). This error indicates that the surrogate pair is incomplete or contains an invalid code point.
json.exception.parse_error.103	parse error: code points above 0x10FFFF are invalid	Unicode supports code points up to 0x10FFFF. Code points above 0x10FFFF are invalid.
json.exception.parse_error.104	parse error: JSON patch must be an array of objects	RFC 6902 requires a JSON Patch document to be a JSON document that represents an array of objects.
json.exception.parse_error.105	parse error: operation must have string member ‘op’	An operation of a JSON Patch document must contain exactly one “op” member, whose value indicates the operation to perform. Its value must be one of “add”, “remove”, “replace”, “move”, “copy”, or “test”; other values are errors.
json.exception.parse_error.106	parse error: array index ‘01’ must not begin with ‘0’	An array index in a JSON Pointer (RFC 6901) may be 0 or any number without a leading 0.
json.exception.parse_error.107	parse error: JSON pointer must be empty or begin with ‘/’ - was: ‘foo’	A JSON Pointer must be a Unicode string containing a sequence of zero or more reference tokens, each prefixed by a / character.
json.exception.parse_error.108	parse error: escape character ‘~’ must be followed with ‘0’ or ‘1’	In a JSON Pointer, only ~0 and ~1 are valid escape sequences.
json.exception.parse_error.109	parse error: array index ‘one’ is not a number	A JSON Pointer array index must be a number.
json.exception.parse_error.110	parse error at 1: cannot read 2 bytes from vector	When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
json.exception.parse_error.112	parse error at 1: error reading CBOR; last byte: 0xF8	Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
json.exception.parse_error.113	parse error at 2: expected a CBOR string; last byte: 0x98	While parsing a map key, a value that is not a string has been read.
json.exception.parse_error.114	parse error: Unsupported BSON record type 0x0F	The parsing of the corresponding BSON record type is not implemented (yet).
json.exception.parse_error.115	parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1A	A UBJSON high-precision number could not be parsed.

@liveexample{The following code shows how a parse_error exception can be caught.,parse_error}

See also

- exception for the base class of the library exceptions

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

Note

For an input with n bytes, 1 is the index of the first character and n+1 is the index of the terminating null byte or the end of file. This also holds true when reading a byte vector (CBOR or MessagePack).

Note

For an input with n bytes, 1 is the index of the first character and n+1 is the index of the terminating null byte or the end of file. This also holds true when reading a byte vector (CBOR or MessagePack).

using invalid_iterator = detail::invalid_iterator

exception indicating errors with iterators

This exception is thrown if iterators passed to a library function do not match the expected semantics.

Exceptions have ids 2xx.

name / id	example message	description
json.exception.invalid_iterator.201	iterators are not compatible	The iterators passed to constructor basic_json(InputIT first, InputIT last) are not compatible, meaning they do not belong to the same container. Therefore, the range (first, last) is invalid.
json.exception.invalid_iterator.202	iterator does not fit current value	In an erase or insert function, the passed iterator pos does not belong to the JSON value for which the function was called. It hence does not define a valid position for the deletion/insertion.
json.exception.invalid_iterator.203	iterators do not fit current value	Either iterator passed to function erase(IteratorType first, IteratorType last) does not belong to the JSON value from which values shall be erased. It hence does not define a valid range to delete values from.
json.exception.invalid_iterator.204	iterators out of range	When an iterator range for a primitive type (number, boolean, or string) is passed to a constructor or an erase function, this range has to be exactly (begin(), end()), because this is the only way the single stored value is expressed. All other ranges are invalid.
json.exception.invalid_iterator.205	iterator out of range	When an iterator for a primitive type (number, boolean, or string) is passed to an erase function, the iterator has to be the begin() iterator, because it is the only way to address the stored value. All other iterators are invalid.
json.exception.invalid_iterator.206	cannot construct with iterators from null	The iterators passed to constructor basic_json(InputIT first, InputIT last) belong to a JSON null value and hence to not define a valid range.
json.exception.invalid_iterator.207	cannot use key() for non-object iterators	The key() member function can only be used on iterators belonging to a JSON object, because other types do not have a concept of a key.
json.exception.invalid_iterator.208	cannot use operator[] for object iterators	The operator[] to specify a concrete offset cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
json.exception.invalid_iterator.209	cannot use offsets with object iterators	The offset operators (+, -, +=, -=) cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
json.exception.invalid_iterator.210	iterators do not fit	The iterator range passed to the insert function are not compatible, meaning they do not belong to the same container. Therefore, the range (first, last) is invalid.
json.exception.invalid_iterator.211	passed iterators may not belong to container	The iterator range passed to the insert function must not be a subrange of the container to insert to.
json.exception.invalid_iterator.212	cannot compare iterators of different containers	When two iterators are compared, they must belong to the same container.
json.exception.invalid_iterator.213	cannot compare order of object iterators	The order of object iterators cannot be compared, because JSON objects are unordered.
json.exception.invalid_iterator.214	cannot get value	Cannot get value for iterator: Either the iterator belongs to a null value or it is an iterator to a primitive type (number, boolean, or string), but the iterator is different to begin().

@liveexample{The following code shows how an invalid_iterator exception can be caught.,invalid_iterator}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

using type_error = detail::type_error

exception indicating executing a member function with a wrong type

This exception is thrown in case of a type error; that is, a library function is executed on a JSON value whose type does not match the expected semantics.

Exceptions have ids 3xx.

name / id	example message	description
json.exception.type_error.301	cannot create object from initializer list	To create an object from an initializer list, the initializer list must consist only of a list of pairs whose first element is a string. When this constraint is violated, an array is created instead.
json.exception.type_error.302	type must be object, but is array	During implicit or explicit value conversion, the JSON type must be compatible to the target type. For instance, a JSON string can only be converted into string types, but not into numbers or boolean types.
json.exception.type_error.303	incompatible ReferenceType for get_ref, actual type is object	To retrieve a reference to a value stored in a basic_json object with get_ref, the type of the reference must match the value type. For instance, for a JSON array, the ReferenceType must be array_t &.
json.exception.type_error.304	cannot use at() with string	The at() member functions can only be executed for certain JSON types.
json.exception.type_error.305	cannot use operator[] with string	The operator[] member functions can only be executed for certain JSON types.
json.exception.type_error.306	cannot use value() with string	The value() member functions can only be executed for certain JSON types.
json.exception.type_error.307	cannot use erase() with string	The erase() member functions can only be executed for certain JSON types.
json.exception.type_error.308	cannot use push_back() with string	The push_back() and operator+= member functions can only be executed for certain JSON types.
json.exception.type_error.309	cannot use insert() with	The insert() member functions can only be executed for certain JSON types.
json.exception.type_error.310	cannot use swap() with number	The swap() member functions can only be executed for certain JSON types.
json.exception.type_error.311	cannot use emplace_back() with string	The emplace_back() member function can only be executed for certain JSON types.
json.exception.type_error.312	cannot use update() with string	The update() member functions can only be executed for certain JSON types.
json.exception.type_error.313	invalid value to unflatten	The unflatten function converts an object whose keys are JSON Pointers back into an arbitrary nested JSON value. The JSON Pointers must not overlap, because then the resulting value would not be well defined.
json.exception.type_error.314	only objects can be unflattened	The unflatten function only works for an object whose keys are JSON Pointers.
json.exception.type_error.315	values in object must be primitive	The unflatten function only works for an object whose keys are JSON Pointers and whose values are primitive.
json.exception.type_error.316	invalid UTF-8 byte at index 10: 0x7E	The dump function only works with UTF-8 encoded strings; that is, if you assign a std::string to a JSON value, make sure it is UTF-8 encoded.
json.exception.type_error.317	JSON value cannot be serialized to requested format	The dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw true or null JSON object cannot be serialized to BSON)

@liveexample{The following code shows how a type_error exception can be caught.,type_error}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

using out_of_range = detail::out_of_range

exception indicating access out of the defined range

This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance in case of array indices or nonexisting object keys.

Exceptions have ids 4xx.

name / id	example message	description
json.exception.out_of_range.401	array index 3 is out of range	The provided array index i is larger than size-1.
json.exception.out_of_range.402	array index ‘-’ (3) is out of range	The special array index - in a JSON Pointer never describes a valid element of the array, but the index past the end. That is, it can only be used to add elements at this position, but not to read it.
json.exception.out_of_range.403	key ‘foo’ not found	The provided key was not found in the JSON object.
json.exception.out_of_range.404	unresolved reference token ‘foo’	A reference token in a JSON Pointer could not be resolved.
json.exception.out_of_range.405	JSON pointer has no parent	The JSON Patch operations ‘remove’ and ‘add’ can not be applied to the root element of the JSON value.
json.exception.out_of_range.406	number overflow parsing ‘10E1000’	A parsed number could not be stored as without changing it to NaN or INF.
json.exception.out_of_range.407	number overflow serializing ‘9223372036854775808’	UBJSON and BSON only support integer numbers up to 9223372036854775807.
json.exception.out_of_range.408	excessive array size: 8658170730974374167	The size (following #) of an UBJSON array or object exceeds the maximal capacity.
json.exception.out_of_range.409	BSON key cannot contain code point U+0000 (at byte 2)	Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string

@liveexample{The following code shows how an out_of_range exception can be caught.,out_of_range}

This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance in case of array indices or nonexisting object keys.

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

Exceptions have ids 4xx.

name / id	example message	description
json.exception.out_of_range.401	array index 3 is out of range	The provided array index i is larger than size-1.
json.exception.out_of_range.402	array index ‘-’ (3) is out of range	The special array index - in a JSON Pointer never describes a valid element of the array, but the index past the end. That is, it can only be used to add elements at this position, but not to read it.
json.exception.out_of_range.403	key ‘foo’ not found	The provided key was not found in the JSON object.
json.exception.out_of_range.404	unresolved reference token ‘foo’	A reference token in a JSON Pointer could not be resolved.
json.exception.out_of_range.405	JSON pointer has no parent	The JSON Patch operations ‘remove’ and ‘add’ can not be applied to the root element of the JSON value.
json.exception.out_of_range.406	number overflow parsing ‘10E1000’	A parsed number could not be stored as without changing it to NaN or INF.
json.exception.out_of_range.407	number overflow serializing ‘9223372036854775808’	UBJSON and BSON only support integer numbers up to 9223372036854775807. (until version 3.8.0)
json.exception.out_of_range.408	excessive array size: 8658170730974374167	The size (following #) of an UBJSON array or object exceeds the maximal capacity.
json.exception.out_of_range.409	BSON key cannot contain code point U+0000 (at byte 2)	Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string

@liveexample{The following code shows how an out_of_range exception can be caught.,out_of_range}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

using other_error = detail::other_error

exception indicating other library errors

This exception is thrown in case of errors that cannot be classified with the other exception types.

Exceptions have ids 5xx.

name / id	example message	description
json.exception.other_error.501	unsuccessful: {“op”:”test”,”path”:”/baz”, “value”:”bar”}	A JSON Patch operation ‘test’ failed. The unsuccessful operation is also printed.

@liveexample{The following code shows how an other_error exception can be caught.,other_error}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

Since

version 3.0.0

using exception = detail::exception

general exception of the basic_json class

This class is an extension of std::exception objects with a member id for exception ids. It is used as the base class for all exceptions thrown by the basic_json class. This class can hence be used as “wildcard” to catch exceptions.

Subclasses:

• parse_error for exceptions indicating a parse error

• invalid_iterator for exceptions indicating errors with iterators

• type_error for exceptions indicating executing a member function with a wrong type

• out_of_range for exceptions indicating access out of the defined range

• other_error for exceptions indicating other library errors

@liveexample{The following code shows how arbitrary library exceptions can be caught.,exception}

Since

version 3.0.0

using parse_error = detail::parse_error

exception indicating a parse error

This exception is thrown by the library when a parse error occurs. Parse errors can occur during the deserialization of JSON text, CBOR, MessagePack, as well as when using JSON Patch.

Member byte holds the byte index of the last read character in the input file.

Exceptions have ids 1xx.

name / id	example message	description
json.exception.parse_error.101	parse error at 2: unexpected end of input; expected string literal	This error indicates a syntax error while deserializing a JSON text. The error message describes that an unexpected token (character) was encountered, and the member byte indicates the error position.
json.exception.parse_error.102	parse error at 14: missing or wrong low surrogate	JSON uses the \uxxxx format to describe Unicode characters. Code points above above 0xFFFF are split into two \uxxxx entries (“surrogate pairs”). This error indicates that the surrogate pair is incomplete or contains an invalid code point.
json.exception.parse_error.103	parse error: code points above 0x10FFFF are invalid	Unicode supports code points up to 0x10FFFF. Code points above 0x10FFFF are invalid.
json.exception.parse_error.104	parse error: JSON patch must be an array of objects	RFC 6902 requires a JSON Patch document to be a JSON document that represents an array of objects.
json.exception.parse_error.105	parse error: operation must have string member ‘op’	An operation of a JSON Patch document must contain exactly one “op” member, whose value indicates the operation to perform. Its value must be one of “add”, “remove”, “replace”, “move”, “copy”, or “test”; other values are errors.
json.exception.parse_error.106	parse error: array index ‘01’ must not begin with ‘0’	An array index in a JSON Pointer (RFC 6901) may be 0 or any number without a leading 0.
json.exception.parse_error.107	parse error: JSON pointer must be empty or begin with ‘/’ - was: ‘foo’	A JSON Pointer must be a Unicode string containing a sequence of zero or more reference tokens, each prefixed by a / character.
json.exception.parse_error.108	parse error: escape character ‘~’ must be followed with ‘0’ or ‘1’	In a JSON Pointer, only ~0 and ~1 are valid escape sequences.
json.exception.parse_error.109	parse error: array index ‘one’ is not a number	A JSON Pointer array index must be a number.
json.exception.parse_error.110	parse error at 1: cannot read 2 bytes from vector	When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
json.exception.parse_error.112	parse error at 1: error reading CBOR; last byte: 0xF8	Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
json.exception.parse_error.113	parse error at 2: expected a CBOR string; last byte: 0x98	While parsing a map key, a value that is not a string has been read.
json.exception.parse_error.114	parse error: Unsupported BSON record type 0x0F	The parsing of the corresponding BSON record type is not implemented (yet).

@liveexample{The following code shows how a parse_error exception can be caught.,parse_error}

This exception is thrown by the library when a parse error occurs. Parse errors can occur during the deserialization of JSON text, CBOR, MessagePack, as well as when using JSON Patch.

See also

- exception for the base class of the library exceptions

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

Member byte holds the byte index of the last read character in the input file.

Exceptions have ids 1xx.

name / id	example message	description
json.exception.parse_error.101	parse error at 2: unexpected end of input; expected string literal	This error indicates a syntax error while deserializing a JSON text. The error message describes that an unexpected token (character) was encountered, and the member byte indicates the error position.
json.exception.parse_error.102	parse error at 14: missing or wrong low surrogate	JSON uses the \uxxxx format to describe Unicode characters. Code points above above 0xFFFF are split into two \uxxxx entries (“surrogate pairs”). This error indicates that the surrogate pair is incomplete or contains an invalid code point.
json.exception.parse_error.103	parse error: code points above 0x10FFFF are invalid	Unicode supports code points up to 0x10FFFF. Code points above 0x10FFFF are invalid.
json.exception.parse_error.104	parse error: JSON patch must be an array of objects	RFC 6902 requires a JSON Patch document to be a JSON document that represents an array of objects.
json.exception.parse_error.105	parse error: operation must have string member ‘op’	An operation of a JSON Patch document must contain exactly one “op” member, whose value indicates the operation to perform. Its value must be one of “add”, “remove”, “replace”, “move”, “copy”, or “test”; other values are errors.
json.exception.parse_error.106	parse error: array index ‘01’ must not begin with ‘0’	An array index in a JSON Pointer (RFC 6901) may be 0 or any number without a leading 0.
json.exception.parse_error.107	parse error: JSON pointer must be empty or begin with ‘/’ - was: ‘foo’	A JSON Pointer must be a Unicode string containing a sequence of zero or more reference tokens, each prefixed by a / character.
json.exception.parse_error.108	parse error: escape character ‘~’ must be followed with ‘0’ or ‘1’	In a JSON Pointer, only ~0 and ~1 are valid escape sequences.
json.exception.parse_error.109	parse error: array index ‘one’ is not a number	A JSON Pointer array index must be a number.
json.exception.parse_error.110	parse error at 1: cannot read 2 bytes from vector	When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
json.exception.parse_error.112	parse error at 1: error reading CBOR; last byte: 0xF8	Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
json.exception.parse_error.113	parse error at 2: expected a CBOR string; last byte: 0x98	While parsing a map key, a value that is not a string has been read.
json.exception.parse_error.114	parse error: Unsupported BSON record type 0x0F	The parsing of the corresponding BSON record type is not implemented (yet).
json.exception.parse_error.115	parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1A	A UBJSON high-precision number could not be parsed.

@liveexample{The following code shows how a parse_error exception can be caught.,parse_error}

See also

- exception for the base class of the library exceptions

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

Note

For an input with n bytes, 1 is the index of the first character and n+1 is the index of the terminating null byte or the end of file. This also holds true when reading a byte vector (CBOR or MessagePack).

Note

For an input with n bytes, 1 is the index of the first character and n+1 is the index of the terminating null byte or the end of file. This also holds true when reading a byte vector (CBOR or MessagePack).

using invalid_iterator = detail::invalid_iterator

exception indicating errors with iterators

This exception is thrown if iterators passed to a library function do not match the expected semantics.

Exceptions have ids 2xx.

name / id	example message	description
json.exception.invalid_iterator.201	iterators are not compatible	The iterators passed to constructor basic_json(InputIT first, InputIT last) are not compatible, meaning they do not belong to the same container. Therefore, the range (first, last) is invalid.
json.exception.invalid_iterator.202	iterator does not fit current value	In an erase or insert function, the passed iterator pos does not belong to the JSON value for which the function was called. It hence does not define a valid position for the deletion/insertion.
json.exception.invalid_iterator.203	iterators do not fit current value	Either iterator passed to function erase(IteratorType first, IteratorType last) does not belong to the JSON value from which values shall be erased. It hence does not define a valid range to delete values from.
json.exception.invalid_iterator.204	iterators out of range	When an iterator range for a primitive type (number, boolean, or string) is passed to a constructor or an erase function, this range has to be exactly (begin(), end()), because this is the only way the single stored value is expressed. All other ranges are invalid.
json.exception.invalid_iterator.205	iterator out of range	When an iterator for a primitive type (number, boolean, or string) is passed to an erase function, the iterator has to be the begin() iterator, because it is the only way to address the stored value. All other iterators are invalid.
json.exception.invalid_iterator.206	cannot construct with iterators from null	The iterators passed to constructor basic_json(InputIT first, InputIT last) belong to a JSON null value and hence to not define a valid range.
json.exception.invalid_iterator.207	cannot use key() for non-object iterators	The key() member function can only be used on iterators belonging to a JSON object, because other types do not have a concept of a key.
json.exception.invalid_iterator.208	cannot use operator[] for object iterators	The operator[] to specify a concrete offset cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
json.exception.invalid_iterator.209	cannot use offsets with object iterators	The offset operators (+, -, +=, -=) cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.
json.exception.invalid_iterator.210	iterators do not fit	The iterator range passed to the insert function are not compatible, meaning they do not belong to the same container. Therefore, the range (first, last) is invalid.
json.exception.invalid_iterator.211	passed iterators may not belong to container	The iterator range passed to the insert function must not be a subrange of the container to insert to.
json.exception.invalid_iterator.212	cannot compare iterators of different containers	When two iterators are compared, they must belong to the same container.
json.exception.invalid_iterator.213	cannot compare order of object iterators	The order of object iterators cannot be compared, because JSON objects are unordered.
json.exception.invalid_iterator.214	cannot get value	Cannot get value for iterator: Either the iterator belongs to a null value or it is an iterator to a primitive type (number, boolean, or string), but the iterator is different to begin().

@liveexample{The following code shows how an invalid_iterator exception can be caught.,invalid_iterator}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

using type_error = detail::type_error

exception indicating executing a member function with a wrong type

This exception is thrown in case of a type error; that is, a library function is executed on a JSON value whose type does not match the expected semantics.

Exceptions have ids 3xx.

name / id	example message	description
json.exception.type_error.301	cannot create object from initializer list	To create an object from an initializer list, the initializer list must consist only of a list of pairs whose first element is a string. When this constraint is violated, an array is created instead.
json.exception.type_error.302	type must be object, but is array	During implicit or explicit value conversion, the JSON type must be compatible to the target type. For instance, a JSON string can only be converted into string types, but not into numbers or boolean types.
json.exception.type_error.303	incompatible ReferenceType for get_ref, actual type is object	To retrieve a reference to a value stored in a basic_json object with get_ref, the type of the reference must match the value type. For instance, for a JSON array, the ReferenceType must be array_t &.
json.exception.type_error.304	cannot use at() with string	The at() member functions can only be executed for certain JSON types.
json.exception.type_error.305	cannot use operator[] with string	The operator[] member functions can only be executed for certain JSON types.
json.exception.type_error.306	cannot use value() with string	The value() member functions can only be executed for certain JSON types.
json.exception.type_error.307	cannot use erase() with string	The erase() member functions can only be executed for certain JSON types.
json.exception.type_error.308	cannot use push_back() with string	The push_back() and operator+= member functions can only be executed for certain JSON types.
json.exception.type_error.309	cannot use insert() with	The insert() member functions can only be executed for certain JSON types.
json.exception.type_error.310	cannot use swap() with number	The swap() member functions can only be executed for certain JSON types.
json.exception.type_error.311	cannot use emplace_back() with string	The emplace_back() member function can only be executed for certain JSON types.
json.exception.type_error.312	cannot use update() with string	The update() member functions can only be executed for certain JSON types.
json.exception.type_error.313	invalid value to unflatten	The unflatten function converts an object whose keys are JSON Pointers back into an arbitrary nested JSON value. The JSON Pointers must not overlap, because then the resulting value would not be well defined.
json.exception.type_error.314	only objects can be unflattened	The unflatten function only works for an object whose keys are JSON Pointers.
json.exception.type_error.315	values in object must be primitive	The unflatten function only works for an object whose keys are JSON Pointers and whose values are primitive.
json.exception.type_error.316	invalid UTF-8 byte at index 10: 0x7E	The dump function only works with UTF-8 encoded strings; that is, if you assign a std::string to a JSON value, make sure it is UTF-8 encoded.
json.exception.type_error.317	JSON value cannot be serialized to requested format	The dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw true or null JSON object cannot be serialized to BSON)

@liveexample{The following code shows how a type_error exception can be caught.,type_error}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- out_of_range for exceptions indicating access out of the defined range

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

using out_of_range = detail::out_of_range

exception indicating access out of the defined range

This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance in case of array indices or nonexisting object keys.

Exceptions have ids 4xx.

name / id	example message	description
json.exception.out_of_range.401	array index 3 is out of range	The provided array index i is larger than size-1.
json.exception.out_of_range.402	array index ‘-’ (3) is out of range	The special array index - in a JSON Pointer never describes a valid element of the array, but the index past the end. That is, it can only be used to add elements at this position, but not to read it.
json.exception.out_of_range.403	key ‘foo’ not found	The provided key was not found in the JSON object.
json.exception.out_of_range.404	unresolved reference token ‘foo’	A reference token in a JSON Pointer could not be resolved.
json.exception.out_of_range.405	JSON pointer has no parent	The JSON Patch operations ‘remove’ and ‘add’ can not be applied to the root element of the JSON value.
json.exception.out_of_range.406	number overflow parsing ‘10E1000’	A parsed number could not be stored as without changing it to NaN or INF.
json.exception.out_of_range.407	number overflow serializing ‘9223372036854775808’	UBJSON and BSON only support integer numbers up to 9223372036854775807.
json.exception.out_of_range.408	excessive array size: 8658170730974374167	The size (following #) of an UBJSON array or object exceeds the maximal capacity.
json.exception.out_of_range.409	BSON key cannot contain code point U+0000 (at byte 2)	Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string

@liveexample{The following code shows how an out_of_range exception can be caught.,out_of_range}

This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance in case of array indices or nonexisting object keys.

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

Exceptions have ids 4xx.

name / id	example message	description
json.exception.out_of_range.401	array index 3 is out of range	The provided array index i is larger than size-1.
json.exception.out_of_range.402	array index ‘-’ (3) is out of range	The special array index - in a JSON Pointer never describes a valid element of the array, but the index past the end. That is, it can only be used to add elements at this position, but not to read it.
json.exception.out_of_range.403	key ‘foo’ not found	The provided key was not found in the JSON object.
json.exception.out_of_range.404	unresolved reference token ‘foo’	A reference token in a JSON Pointer could not be resolved.
json.exception.out_of_range.405	JSON pointer has no parent	The JSON Patch operations ‘remove’ and ‘add’ can not be applied to the root element of the JSON value.
json.exception.out_of_range.406	number overflow parsing ‘10E1000’	A parsed number could not be stored as without changing it to NaN or INF.
json.exception.out_of_range.407	number overflow serializing ‘9223372036854775808’	UBJSON and BSON only support integer numbers up to 9223372036854775807. (until version 3.8.0)
json.exception.out_of_range.408	excessive array size: 8658170730974374167	The size (following #) of an UBJSON array or object exceeds the maximal capacity.
json.exception.out_of_range.409	BSON key cannot contain code point U+0000 (at byte 2)	Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string

@liveexample{The following code shows how an out_of_range exception can be caught.,out_of_range}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- other_error for exceptions indicating other library errors

Since

version 3.0.0

using other_error = detail::other_error

exception indicating other library errors

This exception is thrown in case of errors that cannot be classified with the other exception types.

Exceptions have ids 5xx.

name / id	example message	description
json.exception.other_error.501	unsuccessful: {“op”:”test”,”path”:”/baz”, “value”:”bar”}	A JSON Patch operation ‘test’ failed. The unsuccessful operation is also printed.

@liveexample{The following code shows how an other_error exception can be caught.,other_error}

See also

- exception for the base class of the library exceptions

See also

- parse_error for exceptions indicating a parse error

See also

- invalid_iterator for exceptions indicating errors with iterators

See also

- type_error for exceptions indicating executing a member function with a wrong type

See also

- out_of_range for exceptions indicating access out of the defined range

Since

version 3.0.0

container types

The canonic container types to use basic_json like any other STL container.

using value_type = basic_json

the type of elements in a basic_json container

using reference = value_type&

the type of an element reference

using const_reference = const value_type&

the type of an element const reference

using difference_type = std::ptrdiff_t

a type to represent differences between iterators

using size_type = std::size_t

a type to represent container sizes

using allocator_type = AllocatorType<basic_json>

the allocator type

using pointer = typename std::allocator_traits<allocator_type>::pointer

the type of an element pointer

using const_pointer = typename std::allocator_traits<allocator_type>::const_pointer

the type of an element const pointer

using iterator = iter_impl<basic_json>

an iterator for a basic_json container

using const_iterator = iter_impl<const basic_json>

a const iterator for a basic_json container

using reverse_iterator = json_reverse_iterator<typename basic_json::iterator>

a reverse iterator for a basic_json container

using const_reverse_iterator = json_reverse_iterator<typename basic_json::const_iterator>

a const reverse iterator for a basic_json container

using value_type = basic_json

the type of elements in a basic_json container

using reference = value_type&

the type of an element reference

using const_reference = const value_type&

the type of an element const reference

using difference_type = std::ptrdiff_t

a type to represent differences between iterators

using size_type = std::size_t

a type to represent container sizes

using allocator_type = AllocatorType<basic_json>

the allocator type

using pointer = typename std::allocator_traits<allocator_type>::pointer

the type of an element pointer

using const_pointer = typename std::allocator_traits<allocator_type>::const_pointer

the type of an element const pointer

using iterator = iter_impl<basic_json>

an iterator for a basic_json container

using const_iterator = iter_impl<const basic_json>

a const iterator for a basic_json container

using reverse_iterator = json_reverse_iterator<typename basic_json::iterator>

a reverse iterator for a basic_json container

using const_reverse_iterator = json_reverse_iterator<typename basic_json::const_iterator>

a const reverse iterator for a basic_json container

JSON value data types

The data types to store a JSON value. These types are derived from the template arguments passed to class basic_json.

using object_comparator_t = std::less<StringType>

using object_t = ObjectType<StringType, basic_json, object_comparator_t, AllocatorType<std::pair<const StringType, basic_json>>>

a type for an object

RFC 7159 describes JSON objects as follows:

An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.

To store objects in C++, a type is defined by the template parameters described below.

Template Parameters:

• ObjectType – the container to store objects (e.g., std::map or std::unordered_map)

• StringType – the type of the keys or names (e.g., std::string). The comparison function std::less<StringType> is used to order elements inside the container.

• AllocatorType – the allocator to use for objects (e.g., std::allocator)

using array_t = ArrayType<basic_json, AllocatorType<basic_json>>

a type for an array

RFC 7159 describes JSON arrays as follows:

An array is an ordered sequence of zero or more values.

To store objects in C++, a type is defined by the template parameters explained below.

Template Parameters:

• ArrayType – container type to store arrays (e.g., std::vector or std::list)

• AllocatorType – allocator to use for arrays (e.g., std::allocator)

using string_t = StringType

a type for a string

RFC 7159 describes JSON strings as follows:

A string is a sequence of zero or more Unicode characters.

To store objects in C++, a type is defined by the template parameter described below. Unicode values are split by the JSON class into byte-sized characters during deserialization.

Template Parameters:

StringType – the container to store strings (e.g., std::string). Note this container is used for keys/names in objects, see object_t.

using boolean_t = BooleanType

a type for a boolean

RFC 7159 implicitly describes a boolean as a type which differentiates the two literals true and false.

To store objects in C++, a type is defined by the template parameter BooleanType which chooses the type to use.

using number_integer_t = NumberIntegerType

a type for a number (integer)

RFC 7159 describes numbers as follows:

The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (…) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.

This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.

To store integer numbers in C++, a type is defined by the template parameter NumberIntegerType which chooses the type to use.

using number_unsigned_t = NumberUnsignedType

a type for a number (unsigned)

RFC 7159 describes numbers as follows:

The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (…) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.

This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.

To store unsigned integer numbers in C++, a type is defined by the template parameter NumberUnsignedType which chooses the type to use.

using number_float_t = NumberFloatType

a type for a number (floating-point)

RFC 7159 describes numbers as follows:

The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (…) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.

This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.

To store floating-point numbers in C++, a type is defined by the template parameter NumberFloatType which chooses the type to use.

using object_comparator_t = std::less<StringType>

using object_t = ObjectType<StringType, basic_json, object_comparator_t, AllocatorType<std::pair<const StringType, basic_json>>>

a type for an object

RFC 7159 describes JSON objects as follows:

An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.

To store objects in C++, a type is defined by the template parameters described below.

Template Parameters:

• ObjectType – the container to store objects (e.g., std::map or std::unordered_map)

• StringType – the type of the keys or names (e.g., std::string). The comparison function std::less<StringType> is used to order elements inside the container.

• AllocatorType – the allocator to use for objects (e.g., std::allocator)

using array_t = ArrayType<basic_json, AllocatorType<basic_json>>

a type for an array

RFC 7159 describes JSON arrays as follows:

An array is an ordered sequence of zero or more values.

To store objects in C++, a type is defined by the template parameters explained below.

Template Parameters:

• ArrayType – container type to store arrays (e.g., std::vector or std::list)

• AllocatorType – allocator to use for arrays (e.g., std::allocator)

using string_t = StringType

a type for a string

RFC 7159 describes JSON strings as follows:

A string is a sequence of zero or more Unicode characters.

To store objects in C++, a type is defined by the template parameter described below. Unicode values are split by the JSON class into byte-sized characters during deserialization.

Template Parameters:

StringType – the container to store strings (e.g., std::string). Note this container is used for keys/names in objects, see object_t.

using boolean_t = BooleanType

a type for a boolean

RFC 7159 implicitly describes a boolean as a type which differentiates the two literals true and false.

To store objects in C++, a type is defined by the template parameter BooleanType which chooses the type to use.

using number_integer_t = NumberIntegerType

a type for a number (integer)

RFC 7159 describes numbers as follows:

The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (…) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.

This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.

To store integer numbers in C++, a type is defined by the template parameter NumberIntegerType which chooses the type to use.

using number_unsigned_t = NumberUnsignedType

a type for a number (unsigned)

RFC 7159 describes numbers as follows:

The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (…) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.

This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.

To store unsigned integer numbers in C++, a type is defined by the template parameter NumberUnsignedType which chooses the type to use.

using number_float_t = NumberFloatType

a type for a number (floating-point)

RFC 7159 describes numbers as follows:

The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (…) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.

This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.

To store floating-point numbers in C++, a type is defined by the template parameter NumberFloatType which chooses the type to use.

using binary_t = nlohmann::byte_container_with_subtype<BinaryType>

a type for a packed binary type

This type is a type designed to carry binary data that appears in various serialized formats, such as CBOR’s Major Type 2, MessagePack’s bin, and BSON’s generic binary subtype. This type is NOT a part of standard JSON and exists solely for compatibility with these binary types. As such, it is simply defined as an ordered sequence of zero or more byte values.

Additionally, as an implementation detail, the subtype of the binary data is carried around as a std::uint8_t, which is compatible with both of the binary data formats that use binary subtyping, (though the specific numbering is incompatible with each other, and it is up to the user to translate between them).

CBOR’s RFC 7049 describes this type as:

Major type 2: a byte string. The string’s length in bytes is represented following the rules for positive integers (major type 0).

MessagePack’s documentation on the bin type family describes this type as:

Bin format family stores an byte array in 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.

BSON’s specifications describe several binary types; however, this type is intended to represent the generic binary type which has the description:

Generic binary subtype - This is the most commonly used binary subtype and should be the ‘default’ for drivers and tools.

None of these impose any limitations on the internal representation other than the basic unit of storage be some type of array whose parts are decomposable into bytes.

The default representation of this binary format is a std::vector<std::uint8_t>, which is a very common way to represent a byte array in modern C++.

lexicographical comparison operators

inline friend bool operator==(const_reference lhs, const_reference rhs) noexcept

comparison: equal

Compares two JSON values for equality according to the following rules:

• Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same according to their respective operator==.

• Integer and floating-point numbers are automatically converted before comparison. Note than two NaN values are always treated as unequal.

• Two JSON null values are equal.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Linear.

@liveexample{The example demonstrates comparing several JSON types.,operator__equal}

Since

version 1.0.0

Note

Floating-point inside JSON values numbers are compared with json::number_float_t::operator== which is double::operator== by default. To compare floating-point while respecting an epsilon, an alternative comparison function could be used, for instance

template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
inline bool is_same(T a, T b, T epsilon = std::numeric_limits<T>::epsilon()) noexcept
{
    return std::abs(a - b) <= epsilon;
}

Note

NaN values never compare equal to themselves or to other NaN values.

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator==(const_reference lhs, const ScalarType rhs) noexcept

comparison: equal

comparison: equal

Compares two JSON values for equality according to the following rules:

• Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same according to their respective operator==.

• Integer and floating-point numbers are automatically converted before comparison. Note than two NaN values are always treated as unequal.

• Two JSON null values are equal.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Linear.

@liveexample{The example demonstrates comparing several JSON types.,operator__equal}

Since

version 1.0.0

Note

Floating-point inside JSON values numbers are compared with json::number_float_t::operator== which is double::operator== by default. To compare floating-point while respecting an epsilon, an alternative comparison function could be used, for instance

template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
inline bool is_same(T a, T b, T epsilon = std::numeric_limits<T>::epsilon()) noexcept
{
    return std::abs(a - b) <= epsilon;
}

Note

NaN values never compare equal to themselves or to other NaN values.

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator==(const ScalarType lhs, const_reference rhs) noexcept

comparison: equal

comparison: equal

Compares two JSON values for equality according to the following rules:

• Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same according to their respective operator==.

• Integer and floating-point numbers are automatically converted before comparison. Note than two NaN values are always treated as unequal.

• Two JSON null values are equal.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Linear.

@liveexample{The example demonstrates comparing several JSON types.,operator__equal}

Since

version 1.0.0

Note

Floating-point inside JSON values numbers are compared with json::number_float_t::operator== which is double::operator== by default. To compare floating-point while respecting an epsilon, an alternative comparison function could be used, for instance

template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
inline bool is_same(T a, T b, T epsilon = std::numeric_limits<T>::epsilon()) noexcept
{
    return std::abs(a - b) <= epsilon;
}

Note

NaN values never compare equal to themselves or to other NaN values.

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are equal

inline friend bool operator!=(const_reference lhs, const_reference rhs) noexcept

comparison: not equal

Compares two JSON values for inequality by calculating not (lhs == rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are not equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator!=(const_reference lhs, const ScalarType rhs) noexcept

comparison: not equal

comparison: not equal

Compares two JSON values for inequality by calculating not (lhs == rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are not equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator!=(const ScalarType lhs, const_reference rhs) noexcept

comparison: not equal

comparison: not equal

Compares two JSON values for inequality by calculating not (lhs == rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are not equal

inline friend bool operator<(const_reference lhs, const_reference rhs) noexcept

comparison: less than

Compares whether one JSON value lhs is less than another JSON value rhs according to the following rules:

• If lhs and rhs have the same type, the values are compared using the default < operator.

• Integer and floating-point numbers are automatically converted before comparison

• In case lhs and rhs have different types, the values are ignored and the order of the types is considered, see operator<(const value_t, const value_t).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__less}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<(const_reference lhs, const ScalarType rhs) noexcept

comparison: less than

comparison: less than

Compares whether one JSON value lhs is less than another JSON value rhs according to the following rules:

• If lhs and rhs have the same type, the values are compared using the default < operator.

• Integer and floating-point numbers are automatically converted before comparison

• In case lhs and rhs have different types, the values are ignored and the order of the types is considered, see operator<(const value_t, const value_t).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__less}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<(const ScalarType lhs, const_reference rhs) noexcept

comparison: less than

comparison: less than

Compares whether one JSON value lhs is less than another JSON value rhs according to the following rules:

• If lhs and rhs have the same type, the values are compared using the default < operator.

• Integer and floating-point numbers are automatically converted before comparison

• In case lhs and rhs have different types, the values are ignored and the order of the types is considered, see operator<(const value_t, const value_t).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__less}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than rhs

inline friend bool operator<=(const_reference lhs, const_reference rhs) noexcept

comparison: less than or equal

Compares whether one JSON value lhs is less than or equal to another JSON value by calculating not (rhs < lhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greater}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<=(const_reference lhs, const ScalarType rhs) noexcept

comparison: less than or equal

comparison: less than or equal

Compares whether one JSON value lhs is less than or equal to another JSON value by calculating not (rhs < lhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greater}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<=(const ScalarType lhs, const_reference rhs) noexcept

comparison: less than or equal

comparison: less than or equal

Compares whether one JSON value lhs is less than or equal to another JSON value by calculating not (rhs < lhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greater}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than or equal to rhs

inline friend bool operator>(const_reference lhs, const_reference rhs) noexcept

comparison: greater than

Compares whether one JSON value lhs is greater than another JSON value by calculating not (lhs <= rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__lessequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>(const_reference lhs, const ScalarType rhs) noexcept

comparison: greater than

comparison: greater than

Compares whether one JSON value lhs is greater than another JSON value by calculating not (lhs <= rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__lessequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>(const ScalarType lhs, const_reference rhs) noexcept

comparison: greater than

comparison: greater than

Compares whether one JSON value lhs is greater than another JSON value by calculating not (lhs <= rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__lessequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than to rhs

inline friend bool operator>=(const_reference lhs, const_reference rhs) noexcept

comparison: greater than or equal

Compares whether one JSON value lhs is greater than or equal to another JSON value by calculating not (lhs < rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greaterequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>=(const_reference lhs, const ScalarType rhs) noexcept

comparison: greater than or equal

comparison: greater than or equal

Compares whether one JSON value lhs is greater than or equal to another JSON value by calculating not (lhs < rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greaterequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>=(const ScalarType lhs, const_reference rhs) noexcept

comparison: greater than or equal

comparison: greater than or equal

Compares whether one JSON value lhs is greater than or equal to another JSON value by calculating not (lhs < rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greaterequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than or equal to rhs

inline friend bool operator==(const_reference lhs, const_reference rhs) noexcept

comparison: equal

Compares two JSON values for equality according to the following rules:

• Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same according to their respective operator==.

• Integer and floating-point numbers are automatically converted before comparison. Note that two NaN values are always treated as unequal.

• Two JSON null values are equal.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Linear.

@liveexample{The example demonstrates comparing several JSON types.,operator__equal}

Since

version 1.0.0

Note

Floating-point inside JSON values numbers are compared with json::number_float_t::operator== which is double::operator== by default. To compare floating-point while respecting an epsilon, an alternative comparison function could be used, for instance

template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
inline bool is_same(T a, T b, T epsilon = std::numeric_limits<T>::epsilon()) noexcept
{
    return std::abs(a - b) <= epsilon;
}

Or you can self-defined operator equal function like this:

bool my_equal(const_reference lhs, const_reference rhs) {
const auto lhs_type lhs.type();
const auto rhs_type rhs.type();
if (lhs_type == rhs_type) {
    switch(lhs_type)
        // self_defined case
        case value_t::number_float:
            return std::abs(lhs - rhs) <= std::numeric_limits<float>::epsilon();
        // other cases remain the same with the original
        ...
}
...
}

Note

NaN values never compare equal to themselves or to other NaN values.

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator==(const_reference lhs, const ScalarType rhs) noexcept

comparison: equal

comparison: equal

Compares two JSON values for equality according to the following rules:

• Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same according to their respective operator==.

• Integer and floating-point numbers are automatically converted before comparison. Note than two NaN values are always treated as unequal.

• Two JSON null values are equal.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Linear.

@liveexample{The example demonstrates comparing several JSON types.,operator__equal}

Since

version 1.0.0

Note

Floating-point inside JSON values numbers are compared with json::number_float_t::operator== which is double::operator== by default. To compare floating-point while respecting an epsilon, an alternative comparison function could be used, for instance

template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
inline bool is_same(T a, T b, T epsilon = std::numeric_limits<T>::epsilon()) noexcept
{
    return std::abs(a - b) <= epsilon;
}

Note

NaN values never compare equal to themselves or to other NaN values.

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator==(const ScalarType lhs, const_reference rhs) noexcept

comparison: equal

comparison: equal

Compares two JSON values for equality according to the following rules:

• Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same according to their respective operator==.

• Integer and floating-point numbers are automatically converted before comparison. Note than two NaN values are always treated as unequal.

• Two JSON null values are equal.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Linear.

@liveexample{The example demonstrates comparing several JSON types.,operator__equal}

Since

version 1.0.0

Note

Floating-point inside JSON values numbers are compared with json::number_float_t::operator== which is double::operator== by default. To compare floating-point while respecting an epsilon, an alternative comparison function could be used, for instance

template<typename T, typename = typename std::enable_if<std::is_floating_point<T>::value, T>::type>
inline bool is_same(T a, T b, T epsilon = std::numeric_limits<T>::epsilon()) noexcept
{
    return std::abs(a - b) <= epsilon;
}

Note

NaN values never compare equal to themselves or to other NaN values.

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are equal

inline friend bool operator!=(const_reference lhs, const_reference rhs) noexcept

comparison: not equal

Compares two JSON values for inequality by calculating not (lhs == rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are not equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator!=(const_reference lhs, const ScalarType rhs) noexcept

comparison: not equal

comparison: not equal

Compares two JSON values for inequality by calculating not (lhs == rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are not equal

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator!=(const ScalarType lhs, const_reference rhs) noexcept

comparison: not equal

comparison: not equal

Compares two JSON values for inequality by calculating not (lhs == rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether the values lhs and rhs are not equal

inline friend bool operator<(const_reference lhs, const_reference rhs) noexcept

comparison: less than

Compares whether one JSON value lhs is less than another JSON value rhs according to the following rules:

• If lhs and rhs have the same type, the values are compared using the default < operator.

• Integer and floating-point numbers are automatically converted before comparison

• In case lhs and rhs have different types, the values are ignored and the order of the types is considered, see operator<(const value_t, const value_t).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__less}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<(const_reference lhs, const ScalarType rhs) noexcept

comparison: less than

comparison: less than

Compares whether one JSON value lhs is less than another JSON value rhs according to the following rules:

• If lhs and rhs have the same type, the values are compared using the default < operator.

• Integer and floating-point numbers are automatically converted before comparison

• In case lhs and rhs have different types, the values are ignored and the order of the types is considered, see operator<(const value_t, const value_t).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__less}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<(const ScalarType lhs, const_reference rhs) noexcept

comparison: less than

comparison: less than

Compares whether one JSON value lhs is less than another JSON value rhs according to the following rules:

• If lhs and rhs have the same type, the values are compared using the default < operator.

• Integer and floating-point numbers are automatically converted before comparison

• In case lhs and rhs have different types, the values are ignored and the order of the types is considered, see operator<(const value_t, const value_t).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__less}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than rhs

inline friend bool operator<=(const_reference lhs, const_reference rhs) noexcept

comparison: less than or equal

Compares whether one JSON value lhs is less than or equal to another JSON value by calculating not (rhs < lhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greater}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<=(const_reference lhs, const ScalarType rhs) noexcept

comparison: less than or equal

comparison: less than or equal

Compares whether one JSON value lhs is less than or equal to another JSON value by calculating not (rhs < lhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greater}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator<=(const ScalarType lhs, const_reference rhs) noexcept

comparison: less than or equal

comparison: less than or equal

Compares whether one JSON value lhs is less than or equal to another JSON value by calculating not (rhs < lhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greater}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is less than or equal to rhs

inline friend bool operator>(const_reference lhs, const_reference rhs) noexcept

comparison: greater than

Compares whether one JSON value lhs is greater than another JSON value by calculating not (lhs <= rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__lessequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>(const_reference lhs, const ScalarType rhs) noexcept

comparison: greater than

comparison: greater than

Compares whether one JSON value lhs is greater than another JSON value by calculating not (lhs <= rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__lessequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>(const ScalarType lhs, const_reference rhs) noexcept

comparison: greater than

comparison: greater than

Compares whether one JSON value lhs is greater than another JSON value by calculating not (lhs <= rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__lessequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than to rhs

inline friend bool operator>=(const_reference lhs, const_reference rhs) noexcept

comparison: greater than or equal

Compares whether one JSON value lhs is greater than or equal to another JSON value by calculating not (lhs < rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greaterequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>=(const_reference lhs, const ScalarType rhs) noexcept

comparison: greater than or equal

comparison: greater than or equal

Compares whether one JSON value lhs is greater than or equal to another JSON value by calculating not (lhs < rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greaterequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than or equal to rhs

template<typename ScalarType, typename std::enable_if<std::is_scalar<ScalarType>::value, int>::type = 0>
inline friend bool operator>=(const ScalarType lhs, const_reference rhs) noexcept

comparison: greater than or equal

comparison: greater than or equal

Compares whether one JSON value lhs is greater than or equal to another JSON value by calculating not (lhs < rhs).

@complexity Linear.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@liveexample{The example demonstrates comparing several JSON types.,operator__greaterequal}

Since

version 1.0.0

Parameters:

• lhs – [in] first JSON value to consider

• rhs – [in] second JSON value to consider

Returns:

whether lhs is greater than or equal to rhs

serialization

inline friend std::ostream &operator<<(std::ostream &o, const basic_json &j)

serialize to stream

Serialize the given JSON value j to the output stream o. The JSON value will be serialized using the dump member function.

• The indentation of the output can be controlled with the member variable width of the output stream o. For instance, using the manipulator std::setw(4) on o sets the indentation level to 4 and the serialization result is the same as calling dump(4).

• The indentation character can be controlled with the member variable fill of the output stream o. For instance, the manipulator std::setfill(\t’)` sets indentation to use a tab character rather than the default space character.

@complexity Linear.

@liveexample{The example below shows the serialization with different parameters to width to adjust the indentation level.,operator_serialize}

Since

version 1.0.0; indentation character added in version 3.0.0

Parameters:

• o – [inout] stream to serialize to

• j – [in] JSON value to serialize

Throws:

type_error.316 – if a string stored inside the JSON value is not UTF-8 encoded

Returns:

the stream o

inline friend std::ostream &operator>>(const basic_json &j, std::ostream &o)

serialize to stream

Deprecated:

This stream operator is deprecated and will be removed in future 4.0.0 of the library. Please use operator<<(std::ostream&, const basic_json&) instead; that is, replace calls like j >> o; with o << j;.

Since

version 1.0.0; deprecated since version 3.0.0

inline friend std::ostream &operator<<(std::ostream &o, const basic_json &j)

serialize to stream

Serialize the given JSON value j to the output stream o. The JSON value will be serialized using the dump member function.

• The indentation of the output can be controlled with the member variable width of the output stream o. For instance, using the manipulator std::setw(4) on o sets the indentation level to 4 and the serialization result is the same as calling dump(4).

• The indentation character can be controlled with the member variable fill of the output stream o. For instance, the manipulator std::setfill(\t’)` sets indentation to use a tab character rather than the default space character.

@complexity Linear.

@liveexample{The example below shows the serialization with different parameters to width to adjust the indentation level.,operator_serialize}

Since

version 1.0.0; indentation character added in version 3.0.0

Parameters:

• o – [inout] stream to serialize to

• j – [in] JSON value to serialize

Throws:

type_error.316 – if a string stored inside the JSON value is not UTF-8 encoded

Returns:

the stream o

inline friend std::ostream &operator>>(const basic_json &j, std::ostream &o)

serialize to stream

Deprecated:

This stream operator is deprecated and will be removed in future 4.0.0 of the library. Please use operator<<(std::ostream&, const basic_json&) instead; that is, replace calls like j >> o; with o << j;.

Since

version 1.0.0; deprecated since version 3.0.0

deserialization

inline friend std::istream &operator<<(basic_json &j, std::istream &i)

deserialize from stream

Deprecated:

This stream operator is deprecated and will be removed in version 4.0.0 of the library. Please use operator>>(std::istream&, basic_json&) instead; that is, replace calls like j << i; with i >> j;.

Since

version 1.0.0; deprecated since version 3.0.0

inline friend std::istream &operator>>(std::istream &i, basic_json &j)

deserialize from stream

Deserializes an input stream to a JSON value.

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser.

@liveexample{The example below shows how a JSON value is constructed by reading a serialization from a stream.,operator_deserialize}

See also

parse(std::istream&, const parser_callback_t) for a variant with a parser callback function to filter values while parsing

Since

version 1.0.0

Note

A UTF-8 byte order mark is silently ignored.

Parameters:

• i – [inout] input stream to read a serialized JSON value from

• j – [inout] JSON value to write the deserialized input to

Throws:

• parse_error.101 – in case of an unexpected token

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

inline friend std::istream &operator<<(basic_json &j, std::istream &i)

deserialize from stream

Deprecated:

This stream operator is deprecated and will be removed in version 4.0.0 of the library. Please use operator>>(std::istream&, basic_json&) instead; that is, replace calls like j << i; with i >> j;.

Since

version 1.0.0; deprecated since version 3.0.0

inline friend std::istream &operator>>(std::istream &i, basic_json &j)

deserialize from stream

Deserializes an input stream to a JSON value.

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser.

@liveexample{The example below shows how a JSON value is constructed by reading a serialization from a stream.,operator_deserialize}

See also

parse(std::istream&, const parser_callback_t) for a variant with a parser callback function to filter values while parsing

Since

version 1.0.0

Note

A UTF-8 byte order mark is silently ignored.

Parameters:

• i – [inout] input stream to read a serialized JSON value from

• j – [inout] JSON value to write the deserialized input to

Throws:

• parse_error.101 – in case of an unexpected token

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json parse (detail::input_adapter &&i, const parser_callback_t cb=nullptr, const bool allow_exceptions=true)

deserialize from a compatible input

This function reads from a compatible input. Examples are:

• an array of 1-byte values

• strings with character/literal type with size of 1 byte

• input streams

• container with contiguous storage of 1-byte values. Compatible container types include std::vector, std::string, std::array, std::valarray, and std::initializer_list. Furthermore, C-style arrays can be used with std::begin()/std::end(). User-defined containers can be used as long as they implement random-access iterators and a contiguous storage.

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.

@liveexample{The example below demonstrates the parse() function reading from an array.,parse__array__parser_callback_t}

@liveexample{The example below demonstrates the parse() function with and without callback function.,parse__string__parser_callback_t}

@liveexample{The example below demonstrates the parse() function with and without callback function.,parse__istream__parser_callback_t}

@liveexample{The example below demonstrates the parse() function reading from a contiguous container.,parse__contiguouscontainer__parser_callback_t}

Since

version 2.0.3 (contiguous containers)

Warning

There is no way to enforce all preconditions at compile-time. If the function is called with a noncompliant container and with assertions switched off, the behavior is undefined and will most likely yield segmentation violation.

Note

A UTF-8 byte order mark is silently ignored.

Parameters:

• i – [in] input to read from

• cb – [in] a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.101 – if a parse error occurs; example: ""unexpected end of input; expected string literal""

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

Pre:

Each element of the container has a size of 1 byte. Violating this precondition yields undefined behavior. This precondition is enforced with a static assertion.

Pre:

The container storage is contiguous. Violating this precondition yields undefined behavior. This precondition is enforced with an assertion.

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

static inline bool accept(detail::input_adapter &&i)

template<typename SAX>
static inline bool sax_parse(detail::input_adapter &&i, SAX *sax, input_format_t format = input_format_t::json, const bool strict = true)

generate SAX events

The SAX event lister must follow the interface of json_sax.

This function reads from a compatible input. Examples are:

• an array of 1-byte values

• strings with character/literal type with size of 1 byte

• input streams

• container with contiguous storage of 1-byte values. Compatible container types include std::vector, std::string, std::array, std::valarray, and std::initializer_list. Furthermore, C-style arrays can be used with std::begin()/std::end(). User-defined containers can be used as long as they implement random-access iterators and a contiguous storage.

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the SAX consumer sax has a super-linear complexity.

@liveexample{The example below demonstrates the sax_parse() function reading from string and processing the events with a user-defined SAX event consumer.,sax_parse}

Since

version 3.2.0

Warning

There is no way to enforce all preconditions at compile-time. If the function is called with a noncompliant container and with assertions switched off, the behavior is undefined and will most likely yield segmentation violation.

Note

A UTF-8 byte order mark is silently ignored.

Parameters:

• i – [in] input to read from

• sax – [inout] SAX event listener

• format – [in] the format to parse (JSON, CBOR, MessagePack, or UBJSON)

• strict – [in] whether the input has to be consumed completely

Throws:

• parse_error.101 – if a parse error occurs; example: ""unexpected end of input; expected string literal""

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

Pre:

Each element of the container has a size of 1 byte. Violating this precondition yields undefined behavior. This precondition is enforced with a static assertion.

Pre:

The container storage is contiguous. Violating this precondition yields undefined behavior. This precondition is enforced with an assertion.

Returns:

return value of the last processed SAX event

template<class IteratorType, typename std::enable_if<std::is_base_of<std::random_access_iterator_tag, typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
static inline basic_json parse(IteratorType first, IteratorType last, const parser_callback_t cb = nullptr, const bool allow_exceptions = true)

deserialize from an iterator range with contiguous storage

This function reads from an iterator range of a container with contiguous storage of 1-byte values. Compatible container types include std::vector, std::string, std::array, std::valarray, and std::initializer_list. Furthermore, C-style arrays can be used with std::begin()/std::end(). User-defined containers can be used as long as they implement random-access iterators and a contiguous storage.

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.

@liveexample{The example below demonstrates the parse() function reading from an iterator range.,parse__iteratortype__parser_callback_t}

Since

version 2.0.3

Warning

There is no way to enforce all preconditions at compile-time. If the function is called with noncompliant iterators and with assertions switched off, the behavior is undefined and will most likely yield segmentation violation.

Note

A UTF-8 byte order mark is silently ignored.

Template Parameters:

IteratorType – iterator of container with contiguous storage

Parameters:

• first – [in] begin of the range to parse (included)

• last – [in] end of the range to parse (excluded)

• cb – [in] a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.101 – in case of an unexpected token

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

Pre:

The iterator range is contiguous. Violating this precondition yields undefined behavior. This precondition is enforced with an assertion.

Pre:

Each element in the range has a size of 1 byte. Violating this precondition yields undefined behavior. This precondition is enforced with a static assertion.

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<class IteratorType, typename std::enable_if<std::is_base_of<std::random_access_iterator_tag, typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
static inline bool accept(IteratorType first, IteratorType last)

template<class IteratorType, class SAX, typename std::enable_if<std::is_base_of<std::random_access_iterator_tag, typename std::iterator_traits<IteratorType>::iterator_category>::value, int>::type = 0>
static inline bool sax_parse(IteratorType first, IteratorType last, SAX *sax)

template<typename InputType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json parse (InputType &&i, const parser_callback_t cb=nullptr, const bool allow_exceptions=true, const bool ignore_comments=false)

deserialize from a compatible input

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb or reading from the input i has a super-linear complexity.

@liveexample{The example below demonstrates the parse() function reading from an array.,parse__array__parser_callback_t}

@liveexample{The example below demonstrates the parse() function with and without callback function.,parse__string__parser_callback_t}

@liveexample{The example below demonstrates the parse() function with and without callback function.,parse__istream__parser_callback_t}

@liveexample{The example below demonstrates the parse() function reading from a contiguous container.,parse__contiguouscontainer__parser_callback_t}

Since

version 2.0.3 (contiguous containers); version 3.9.0 allowed to ignore comments.

Note

A UTF-8 byte order mark is silently ignored.

Template Parameters:

InputType – A compatible input, for instance

• an std::istream object

• a FILE pointer

• a C-style array of characters

• a pointer to a null-terminated string of single byte characters

• an object obj for which begin(obj) and end(obj) produces a valid pair of iterators.

Parameters:

• i – [in] input to read from

• cb – [in] a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

• ignore_comments – [in] whether comments should be ignored and treated like whitespace (true) or yield a parse error (true); (optional, false by default)

Throws:

• parse_error.101 – if a parse error occurs; example: ""unexpected end of input; expected string literal""

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename IteratorType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json parse (IteratorType first, IteratorType last, const parser_callback_t cb=nullptr, const bool allow_exceptions=true, const bool ignore_comments=false)

deserialize from a pair of character iterators

The value_type of the iterator must be a integral type with size of 1, 2 or 4 bytes, which will be interpreted respectively as UTF-8, UTF-16 and UTF-32.

Parameters:

• first – [in] iterator to start of character range

• last – [in] iterator to end of character range

• cb – [in] a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

• ignore_comments – [in] whether comments should be ignored and treated like whitespace (true) or yield a parse error (true); (optional, false by default)

Throws:

• parse_error.101 – if a parse error occurs; example: ""unexpected end of input; expected string literal""

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json parse (detail::span_input_adapter &&i, const parser_callback_t cb=nullptr, const bool allow_exceptions=true, const bool ignore_comments=false)

template<typename InputType>
static inline bool accept(InputType &&i, const bool ignore_comments = false)

check if the input is valid JSON

Unlike the parse(InputType&&, const parser_callback_t,const bool) function, this function neither throws an exception in case of invalid JSON input (i.e., a parse error) nor creates diagnostic information.

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser.

@liveexample{The example below demonstrates the accept() function reading from a string.,accept__string}

Note

A UTF-8 byte order mark is silently ignored.

Template Parameters:

InputType – A compatible input, for instance

• an std::istream object

• a FILE pointer

• a C-style array of characters

• a pointer to a null-terminated string of single byte characters

• an object obj for which begin(obj) and end(obj) produces a valid pair of iterators.

Parameters:

• i – [in] input to read from

• ignore_comments – [in] whether comments should be ignored and treated like whitespace (true) or yield a parse error (true); (optional, false by default)

Returns:

Whether the input read from i is valid JSON.

template<typename IteratorType>
static inline bool accept(IteratorType first, IteratorType last, const bool ignore_comments = false)

static inline JSON_HEDLEY_WARN_UNUSED_RESULT bool accept (detail::span_input_adapter &&i, const bool ignore_comments=false)

template<typename InputType, typename SAX>
static inline bool sax_parse(InputType &&i, SAX *sax, input_format_t format = input_format_t::json, const bool strict = true, const bool ignore_comments = false)

generate SAX events

The SAX event lister must follow the interface of json_sax.

This function reads from a compatible input. Examples are:

• an std::istream object

• a FILE pointer

• a C-style array of characters

• a pointer to a null-terminated string of single byte characters

• an object obj for which begin(obj) and end(obj) produces a valid pair of iterators.

@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the SAX consumer sax has a super-linear complexity.

@liveexample{The example below demonstrates the sax_parse() function reading from string and processing the events with a user-defined SAX event consumer.,sax_parse}

Since

version 3.2.0

Note

A UTF-8 byte order mark is silently ignored.

Parameters:

• i – [in] input to read from

• sax – [inout] SAX event listener

• format – [in] the format to parse (JSON, CBOR, MessagePack, or UBJSON)

• strict – [in] whether the input has to be consumed completely

• ignore_comments – [in] whether comments should be ignored and treated like whitespace (true) or yield a parse error (true); (optional, false by default); only applies to the JSON file format.

Throws:

• parse_error.101 – if a parse error occurs; example: ""unexpected end of input; expected string literal""

• parse_error.102 – if to_unicode fails or surrogate error

• parse_error.103 – if to_unicode fails

Returns:

return value of the last processed SAX event

template<class IteratorType, class SAX>
static inline bool sax_parse(IteratorType first, IteratorType last, SAX *sax, input_format_t format = input_format_t::json, const bool strict = true, const bool ignore_comments = false)

template<typename SAX>
static inline bool sax_parse(detail::span_input_adapter &&i, SAX *sax, input_format_t format = input_format_t::json, const bool strict = true, const bool ignore_comments = false)

modifiers

inline friend void swap(reference left, reference right) noexcept(std::is_nothrow_move_constructible<value_t>::value && std::is_nothrow_move_assignable<value_t>::value && std::is_nothrow_move_constructible<json_value>::value && std::is_nothrow_move_assignable<json_value>::value)

exchanges the values

Exchanges the contents of the JSON value from left with those of right. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. implemented as a friend function callable via ADL.

@complexity Constant.

@liveexample{The example below shows how JSON values can be swapped with swap().,swap__reference}

Since

version 1.0.0

Parameters:

• left – [inout] JSON value to exchange the contents with

• right – [inout] JSON value to exchange the contents with

inline void clear() noexcept

clears the contents

Clears the content of a JSON value and resets it to the default value as if basic_json(value_t) would have been called with the current value type from type():

Value type	initial value
null	null
boolean	false
string	""
number	0
object	{}
array	[]

@liveexample{The example below shows the effect of clear() to different JSON types.,clear}

@complexity Linear in the size of the JSON value.

@iterators All iterators, pointers and references related to this container are invalidated.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

See also

basic_json(value_t) &#8212; constructor that creates an object with the same value than calling clear()

Since

version 1.0.0

Post:

Has the same effect as calling

*this = basic_json(type());

inline void push_back(basic_json &&val)

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline reference operator+=(basic_json &&val)

add an object to an array

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline void push_back(const basic_json &val)

add an object to an array

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline reference operator+=(const basic_json &val)

add an object to an array

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline void push_back(const typename object_t::value_type &val)

add an object to an object

Inserts the given element val to the JSON object. If the function is called on a JSON null value, an empty object is created before inserting val.

@complexity Logarithmic in the size of the container, O(log(size())).

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object.,push_back__object_t__value}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON object

Throws:

type_error.308 – when called on a type other than JSON object or null; example: "cannot use push_back() with number"

inline reference operator+=(const typename object_t::value_type &val)

add an object to an object

add an object to an object

Inserts the given element val to the JSON object. If the function is called on a JSON null value, an empty object is created before inserting val.

@complexity Logarithmic in the size of the container, O(log(size())).

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object.,push_back__object_t__value}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON object

Throws:

type_error.308 – when called on a type other than JSON object or null; example: "cannot use push_back() with number"

inline void push_back(initializer_list_t init)

add an object to an object

This function allows to use push_back with an initializer list. In case

1. the current value is an object,

2. the initializer list init contains only two elements, and

3. the first element of init is a string,

init is converted into an object element and added using push_back(const typename object_t::value_type&). Otherwise, init is converted to a JSON value and added using push_back(basic_json&&).

@complexity Linear in the size of the initializer list init.

@liveexample{The example shows how initializer lists are treated as objects when possible.,push_back__initializer_list}

Note

This function is required to resolve an ambiguous overload error, because pairs like {"key", "value"} can be both interpreted as object_t::value_type or std::initializer_list<basic_json>, see https://github.com/nlohmann/json/issues/235 for more information.

Parameters:

init – [in] an initializer list

inline reference operator+=(initializer_list_t init)

add an object to an object

add an object to an object

This function allows to use push_back with an initializer list. In case

1. the current value is an object,

2. the initializer list init contains only two elements, and

3. the first element of init is a string,

init is converted into an object element and added using push_back(const typename object_t::value_type&). Otherwise, init is converted to a JSON value and added using push_back(basic_json&&).

@complexity Linear in the size of the initializer list init.

@liveexample{The example shows how initializer lists are treated as objects when possible.,push_back__initializer_list}

Note

This function is required to resolve an ambiguous overload error, because pairs like {"key", "value"} can be both interpreted as object_t::value_type or std::initializer_list<basic_json>, see https://github.com/nlohmann/json/issues/235 for more information.

Parameters:

init – [in] an initializer list

template<class ...Args>
inline reference emplace_back(Args&&... args)

add an object to an array

Creates a JSON value from the passed parameters args to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending the value created from args.

@complexity Amortized constant.

@liveexample{The example shows how push_back() can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,emplace_back}

Since

version 2.0.8, returns reference since 3.7.0

Parameters:

args – [in] arguments to forward to a constructor of basic_json

Template Parameters:

Args – compatible types to create a basic_json object

Throws:

type_error.311 – when called on a type other than JSON array or null; example: "cannot use emplace_back() with number"

Returns:

reference to the inserted element

template<class ...Args>
inline std::pair<iterator, bool> emplace(Args&&... args)

add an object to an object if key does not exist

Inserts a new element into a JSON object constructed in-place with the given args if there is no element with the key in the container. If the function is called on a JSON null value, an empty object is created before appending the value created from args.

@complexity Logarithmic in the size of the container, O(log(size())).

@liveexample{The example shows how emplace() can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object. Further note how no value is added if there was already one value stored with the same key.,emplace}

Since

version 2.0.8

Parameters:

args – [in] arguments to forward to a constructor of basic_json

Template Parameters:

Args – compatible types to create a basic_json object

Throws:

type_error.311 – when called on a type other than JSON object or null; example: "cannot use emplace() with number"

Returns:

a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a bool denoting whether the insertion took place.

template<typename ...Args>
inline iterator insert_iterator(const_iterator pos, Args&&... args)

Helper for insertion of an iterator

Note

: This uses std::distance to support GCC 4.8, see https://github.com/nlohmann/json/pull/1257

inline iterator insert(const_iterator pos, const basic_json &val)

inserts element

Inserts element val before iterator pos.

@complexity Constant plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• val – [in] element to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the inserted val.

inline iterator insert(const_iterator pos, basic_json &&val)

inserts element

inserts element

Inserts element val before iterator pos.

@complexity Constant plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• val – [in] element to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the inserted val.

inline iterator insert(const_iterator pos, size_type cnt, const basic_json &val)

inserts elements

Inserts cnt copies of val before iterator pos.

@complexity Linear in cnt plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert__count}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• cnt – [in] number of copies of val to insert

• val – [in] element to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the first element inserted, or pos if cnt==0

inline iterator insert(const_iterator pos, const_iterator first, const_iterator last)

inserts elements

Inserts elements from range [first, last) before iterator pos.

@complexity Linear in std::distance(first, last) plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert__range}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• first – [in] begin of the range of elements to insert

• last – [in] end of the range of elements to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

• invalid_iterator.210 – if first and last do not belong to the same JSON value; example: "iterators do not fit"

• invalid_iterator.211 – if first or last are iterators into container for which insert is called; example:

  "passed iterators may not

  belong to container"

Returns:

iterator pointing to the first element inserted, or pos if first==last

inline iterator insert(const_iterator pos, initializer_list_t ilist)

inserts elements

Inserts elements from initializer list ilist before iterator pos.

@complexity Linear in ilist.size() plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert__ilist}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• ilist – [in] initializer list to insert the values from

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the first element inserted, or pos if ilist is empty

inline void insert(const_iterator first, const_iterator last)

inserts elements

Inserts elements from range [first, last).

@complexity Logarithmic: O(N*log(size() + N)), where N is the number of elements to insert.

@liveexample{The example shows how insert() is used.,insert__range_object}

Since

version 3.0.0

Parameters:

• first – [in] begin of the range of elements to insert

• last – [in] end of the range of elements to insert

Throws:

• type_error.309 – if called on JSON values other than objects; example: "cannot use insert() with string"

• invalid_iterator.202 – if iterator first or last does does not point to an object; example:

  "iterators first and last must point to

  objects"

• invalid_iterator.210 – if first and last do not belong to the same JSON value; example: "iterators do not fit"

inline void update(const_reference j)

updates a JSON object from another object, overwriting existing keys

Inserts all values from JSON object j and overwrites existing keys.

@complexity O(N*log(size() + N)), where N is the number of elements to insert.

@liveexample{The example shows how update() is used.,update}

See also

https://docs.python.org/3.6/library/stdtypes.html#dict.update

Since

version 3.0.0

Parameters:

j – [in] JSON object to read values from

Throws:

type_error.312 – if called on JSON values other than objects; example: "cannot use update() with string"

inline void update(const_iterator first, const_iterator last)

updates a JSON object from another object, overwriting existing keys

Inserts all values from from range [first, last) and overwrites existing keys.

@complexity O(N*log(size() + N)), where N is the number of elements to insert.

@liveexample{The example shows how update() is used__range.,update}

See also

https://docs.python.org/3.6/library/stdtypes.html#dict.update

Since

version 3.0.0

Parameters:

• first – [in] begin of the range of elements to insert

• last – [in] end of the range of elements to insert

Throws:

• type_error.312 – if called on JSON values other than objects; example: "cannot use update() with string"

• invalid_iterator.202 – if iterator first or last does does not point to an object; example:

  "iterators first and last must point to

  objects"

• invalid_iterator.210 – if first and last do not belong to the same JSON value; example: "iterators do not fit"

inline void swap(reference other) noexcept(std::is_nothrow_move_constructible<value_t>::value and std::is_nothrow_move_assignable<value_t>::value and std::is_nothrow_move_constructible<json_value>::value and std::is_nothrow_move_assignable<json_value>::value)

exchanges the values

Exchanges the contents of the JSON value with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how JSON values can be swapped with swap().,swap__reference}

Since

version 1.0.0

Parameters:

other – [inout] JSON value to exchange the contents with

inline void swap(array_t &other)

exchanges the values

Exchanges the contents of a JSON array with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how arrays can be swapped with swap().,swap__array_t}

Since

version 1.0.0

Parameters:

other – [inout] array to exchange the contents with

Throws:

type_error.310 – when JSON value is not an array; example:

"cannot

use swap() with string"

inline void swap(object_t &other)

exchanges the values

Exchanges the contents of a JSON object with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how objects can be swapped with swap().,swap__object_t}

Since

version 1.0.0

Parameters:

other – [inout] object to exchange the contents with

Throws:

type_error.310 – when JSON value is not an object; example: "cannot use swap() with string"

inline void swap(string_t &other)

exchanges the values

Exchanges the contents of a JSON string with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how strings can be swapped with swap().,swap__string_t}

Since

version 1.0.0

Parameters:

other – [inout] string to exchange the contents with

Throws:

type_error.310 – when JSON value is not a string; example:

"cannot

use swap() with boolean"

inline void clear() noexcept

clears the contents

Clears the content of a JSON value and resets it to the default value as if basic_json(value_t) would have been called with the current value type from type():

Value type	initial value
null	null
boolean	false
string	""
number	0
binary	An empty byte vector
object	{}
array	[]

@liveexample{The example below shows the effect of clear() to different JSON types.,clear}

@complexity Linear in the size of the JSON value.

@iterators All iterators, pointers and references related to this container are invalidated.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

See also

basic_json(value_t) &#8212; constructor that creates an object with the same value than calling clear()

Since

version 1.0.0

Post:

Has the same effect as calling

*this = basic_json(type());

inline void push_back(basic_json &&val)

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline reference operator+=(basic_json &&val)

add an object to an array

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline void push_back(const basic_json &val)

add an object to an array

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline reference operator+=(const basic_json &val)

add an object to an array

add an object to an array

Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.

@complexity Amortized constant.

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON array

Throws:

type_error.308 – when called on a type other than JSON array or null; example: "cannot use push_back() with number"

inline void push_back(const typename object_t::value_type &val)

add an object to an object

Inserts the given element val to the JSON object. If the function is called on a JSON null value, an empty object is created before inserting val.

@complexity Logarithmic in the size of the container, O(log(size())).

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object.,push_back__object_t__value}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON object

Throws:

type_error.308 – when called on a type other than JSON object or null; example: "cannot use push_back() with number"

inline reference operator+=(const typename object_t::value_type &val)

add an object to an object

add an object to an object

Inserts the given element val to the JSON object. If the function is called on a JSON null value, an empty object is created before inserting val.

@complexity Logarithmic in the size of the container, O(log(size())).

@liveexample{The example shows how push_back() and += can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object.,push_back__object_t__value}

Since

version 1.0.0

Parameters:

val – [in] the value to add to the JSON object

Throws:

type_error.308 – when called on a type other than JSON object or null; example: "cannot use push_back() with number"

inline void push_back(initializer_list_t init)

add an object to an object

This function allows to use push_back with an initializer list. In case

1. the current value is an object,

2. the initializer list init contains only two elements, and

3. the first element of init is a string,

init is converted into an object element and added using push_back(const typename object_t::value_type&). Otherwise, init is converted to a JSON value and added using push_back(basic_json&&).

@complexity Linear in the size of the initializer list init.

@liveexample{The example shows how initializer lists are treated as objects when possible.,push_back__initializer_list}

Note

This function is required to resolve an ambiguous overload error, because pairs like {"key", "value"} can be both interpreted as object_t::value_type or std::initializer_list<basic_json>, see https://github.com/nlohmann/json/issues/235 for more information.

Parameters:

init – [in] an initializer list

inline reference operator+=(initializer_list_t init)

add an object to an object

add an object to an object

This function allows to use push_back with an initializer list. In case

1. the current value is an object,

2. the initializer list init contains only two elements, and

3. the first element of init is a string,

init is converted into an object element and added using push_back(const typename object_t::value_type&). Otherwise, init is converted to a JSON value and added using push_back(basic_json&&).

@complexity Linear in the size of the initializer list init.

@liveexample{The example shows how initializer lists are treated as objects when possible.,push_back__initializer_list}

Note

This function is required to resolve an ambiguous overload error, because pairs like {"key", "value"} can be both interpreted as object_t::value_type or std::initializer_list<basic_json>, see https://github.com/nlohmann/json/issues/235 for more information.

Parameters:

init – [in] an initializer list

template<class ...Args>
inline reference emplace_back(Args&&... args)

add an object to an array

Creates a JSON value from the passed parameters args to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending the value created from args.

@complexity Amortized constant.

@liveexample{The example shows how push_back() can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,emplace_back}

Since

version 2.0.8, returns reference since 3.7.0

Parameters:

args – [in] arguments to forward to a constructor of basic_json

Template Parameters:

Args – compatible types to create a basic_json object

Throws:

type_error.311 – when called on a type other than JSON array or null; example: "cannot use emplace_back() with number"

Returns:

reference to the inserted element

template<class ...Args>
inline std::pair<iterator, bool> emplace(Args&&... args)

add an object to an object if key does not exist

Inserts a new element into a JSON object constructed in-place with the given args if there is no element with the key in the container. If the function is called on a JSON null value, an empty object is created before appending the value created from args.

@complexity Logarithmic in the size of the container, O(log(size())).

@liveexample{The example shows how emplace() can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object. Further note how no value is added if there was already one value stored with the same key.,emplace}

Since

version 2.0.8

Parameters:

args – [in] arguments to forward to a constructor of basic_json

Template Parameters:

Args – compatible types to create a basic_json object

Throws:

type_error.311 – when called on a type other than JSON object or null; example: "cannot use emplace() with number"

Returns:

a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a bool denoting whether the insertion took place.

template<typename ...Args>
inline iterator insert_iterator(const_iterator pos, Args&&... args)

Helper for insertion of an iterator

Note

: This uses std::distance to support GCC 4.8, see https://github.com/nlohmann/json/pull/1257

inline iterator insert(const_iterator pos, const basic_json &val)

inserts element

Inserts element val before iterator pos.

@complexity Constant plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• val – [in] element to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the inserted val.

inline iterator insert(const_iterator pos, basic_json &&val)

inserts element

inserts element

Inserts element val before iterator pos.

@complexity Constant plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• val – [in] element to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the inserted val.

inline iterator insert(const_iterator pos, size_type cnt, const basic_json &val)

inserts elements

Inserts cnt copies of val before iterator pos.

@complexity Linear in cnt plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert__count}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• cnt – [in] number of copies of val to insert

• val – [in] element to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the first element inserted, or pos if cnt==0

inline iterator insert(const_iterator pos, const_iterator first, const_iterator last)

inserts elements

Inserts elements from range [first, last) before iterator pos.

@complexity Linear in std::distance(first, last) plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert__range}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• first – [in] begin of the range of elements to insert

• last – [in] end of the range of elements to insert

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

• invalid_iterator.210 – if first and last do not belong to the same JSON value; example: "iterators do not fit"

• invalid_iterator.211 – if first or last are iterators into container for which insert is called; example:

  "passed iterators may not

  belong to container"

Returns:

iterator pointing to the first element inserted, or pos if first==last

inline iterator insert(const_iterator pos, initializer_list_t ilist)

inserts elements

Inserts elements from initializer list ilist before iterator pos.

@complexity Linear in ilist.size() plus linear in the distance between pos and end of the container.

@liveexample{The example shows how insert() is used.,insert__ilist}

Since

version 1.0.0

Parameters:

• pos – [in] iterator before which the content will be inserted; may be the end() iterator

• ilist – [in] initializer list to insert the values from

Throws:

• type_error.309 – if called on JSON values other than arrays; example: "cannot use insert() with string"

• invalid_iterator.202 – if pos is not an iterator of *this; example: "iterator does not fit current value"

Returns:

iterator pointing to the first element inserted, or pos if ilist is empty

inline void insert(const_iterator first, const_iterator last)

inserts elements

Inserts elements from range [first, last).

@complexity Logarithmic: O(N*log(size() + N)), where N is the number of elements to insert.

@liveexample{The example shows how insert() is used.,insert__range_object}

Since

version 3.0.0

Parameters:

• first – [in] begin of the range of elements to insert

• last – [in] end of the range of elements to insert

Throws:

• type_error.309 – if called on JSON values other than objects; example: "cannot use insert() with string"

• invalid_iterator.202 – if iterator first or last does does not point to an object; example:

  "iterators first and last must point to

  objects"

• invalid_iterator.210 – if first and last do not belong to the same JSON value; example: "iterators do not fit"

inline void update(const_reference j)

updates a JSON object from another object, overwriting existing keys

Inserts all values from JSON object j and overwrites existing keys.

@complexity O(N*log(size() + N)), where N is the number of elements to insert.

@liveexample{The example shows how update() is used.,update}

See also

https://docs.python.org/3.6/library/stdtypes.html#dict.update

Since

version 3.0.0

Parameters:

j – [in] JSON object to read values from

Throws:

type_error.312 – if called on JSON values other than objects; example: "cannot use update() with string"

inline void update(const_iterator first, const_iterator last)

updates a JSON object from another object, overwriting existing keys

Inserts all values from from range [first, last) and overwrites existing keys.

@complexity O(N*log(size() + N)), where N is the number of elements to insert.

@liveexample{The example shows how update() is used__range.,update}

See also

https://docs.python.org/3.6/library/stdtypes.html#dict.update

Since

version 3.0.0

Parameters:

• first – [in] begin of the range of elements to insert

• last – [in] end of the range of elements to insert

Throws:

• type_error.312 – if called on JSON values other than objects; example: "cannot use update() with string"

• invalid_iterator.202 – if iterator first or last does does not point to an object; example:

  "iterators first and last must point to

  objects"

• invalid_iterator.210 – if first and last do not belong to the same JSON value; example: "iterators do not fit"

inline void swap(reference other) noexcept(std::is_nothrow_move_constructible<value_t>::value && std::is_nothrow_move_assignable<value_t>::value && std::is_nothrow_move_constructible<json_value>::value && std::is_nothrow_move_assignable<json_value>::value)

exchanges the values

Exchanges the contents of the JSON value with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how JSON values can be swapped with swap().,swap__reference}

Since

version 1.0.0

Parameters:

other – [inout] JSON value to exchange the contents with

inline void swap(array_t &other)

exchanges the values

Exchanges the contents of a JSON array with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how arrays can be swapped with swap().,swap__array_t}

Since

version 1.0.0

Parameters:

other – [inout] array to exchange the contents with

Throws:

type_error.310 – when JSON value is not an array; example:

"cannot

use swap() with string"

inline void swap(object_t &other)

exchanges the values

Exchanges the contents of a JSON object with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how objects can be swapped with swap().,swap__object_t}

Since

version 1.0.0

Parameters:

other – [inout] object to exchange the contents with

Throws:

type_error.310 – when JSON value is not an object; example: "cannot use swap() with string"

inline void swap(string_t &other)

exchanges the values

Exchanges the contents of a JSON string with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how strings can be swapped with swap().,swap__string_t}

Since

version 1.0.0

Parameters:

other – [inout] string to exchange the contents with

Throws:

type_error.310 – when JSON value is not a string; example:

"cannot

use swap() with boolean"

inline void swap(binary_t &other)

exchanges the values

Exchanges the contents of a JSON string with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

@complexity Constant.

@liveexample{The example below shows how strings can be swapped with swap().,swap__binary_t}

Since

version 3.8.0

Parameters:

other – [inout] binary to exchange the contents with

Throws:

type_error.310 – when JSON value is not a string; example:

"cannot

use swap() with boolean"

inline void swap(typename binary_t::container_type &other)

exchanges the values

Exchanges the contents of the JSON value from left with those of right. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. implemented as a friend function callable via ADL.

@complexity Constant.

@liveexample{The example below shows how JSON values can be swapped with swap().,swap__reference}

Since

version 1.0.0

Parameters:

• left – [inout] JSON value to exchange the contents with

• right – [inout] JSON value to exchange the contents with

constructors and destructors

Constructors of class basic_json, copy/move constructor, copy assignment, static functions creating objects, and the destructor.

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json array (initializer_list_t init={})

explicitly create an array from an initializer list

Creates a JSON array value from a given initializer list. That is, given a list of values a, b, c, creates the JSON value [a, b, c]. If the initializer list is empty, the empty array [] is created.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows an example for the array function.,array}

See also

basic_json(initializer_list_t, bool, value_t) &#8212; create a JSON value from an initializer list

See also

object(initializer_list_t) &#8212; create a JSON object value from an initializer list

Since

version 1.0.0

Note

This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (basic_json(initializer_list_t, bool, value_t)). These cases are:

1. creating an array whose elements are all pairs whose first element is a string &#8212; in this case, the initializer list constructor would create an object, taking the first elements as keys

2. creating an empty array &#8212; passing the empty initializer list to the initializer list constructor yields an empty object

Parameters:

init – [in] initializer list with JSON values to create an array from (optional)

Returns:

JSON array value

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json object (initializer_list_t init={})

explicitly create an object from an initializer list

Creates a JSON object value from a given initializer list. The initializer lists elements must be pairs, and their first elements must be strings. If the initializer list is empty, the empty object {} is created.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows an example for the object function.,object}

See also

basic_json(initializer_list_t, bool, value_t) &#8212; create a JSON value from an initializer list

See also

array(initializer_list_t) &#8212; create a JSON array value from an initializer list

Since

version 1.0.0

Note

This function is only added for symmetry reasons. In contrast to the related function array(initializer_list_t), there are no cases which can only be expressed by this function. That is, any initializer list init can also be passed to the initializer list constructor basic_json(initializer_list_t, bool, value_t).

Parameters:

init – [in] initializer list to create an object from (optional)

Throws:

type_error.301 – if init is not a list of pairs whose first elements are strings. In this case, no object can be created. When such a value is passed to basic_json(initializer_list_t, bool, value_t), an array would have been created from the passed initializer list init. See example below.

Returns:

JSON object value

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json binary (const typename binary_t::container_type &init)

explicitly create a binary array (without subtype)

Creates a JSON binary array value from a given binary container. Binary values are part of various binary formats, such as CBOR, MessagePack, and BSON. This constructor is used to create a value for serialization to those formats.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

Since

version 3.8.0

Note

Note, this function exists because of the difficulty in correctly specifying the correct template overload in the standard value ctor, as both JSON arrays and JSON binary arrays are backed with some form of a std::vector. Because JSON binary arrays are a non-standard extension it was decided that it would be best to prevent automatic initialization of a binary array type, for backwards compatibility and so it does not happen on accident.

Parameters:

init – [in] container containing bytes to use as binary type

Returns:

JSON binary array value

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json binary (const typename binary_t::container_type &init, std::uint8_t subtype)

explicitly create a binary array (with subtype)

Creates a JSON binary array value from a given binary container. Binary values are part of various binary formats, such as CBOR, MessagePack, and BSON. This constructor is used to create a value for serialization to those formats.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

Since

version 3.8.0

Note

Note, this function exists because of the difficulty in correctly specifying the correct template overload in the standard value ctor, as both JSON arrays and JSON binary arrays are backed with some form of a std::vector. Because JSON binary arrays are a non-standard extension it was decided that it would be best to prevent automatic initialization of a binary array type, for backwards compatibility and so it does not happen on accident.

Parameters:

• init – [in] container containing bytes to use as binary type

• subtype – [in] subtype to use in MessagePack and BSON

Returns:

JSON binary array value

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json binary (typename binary_t::container_type &&init)

explicitly create a binary array (without subtype)

Creates a JSON binary array value from a given binary container. Binary values are part of various binary formats, such as CBOR, MessagePack, and BSON. This constructor is used to create a value for serialization to those formats.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

Since

version 3.8.0

Note

Note, this function exists because of the difficulty in correctly specifying the correct template overload in the standard value ctor, as both JSON arrays and JSON binary arrays are backed with some form of a std::vector. Because JSON binary arrays are a non-standard extension it was decided that it would be best to prevent automatic initialization of a binary array type, for backwards compatibility and so it does not happen on accident.

Parameters:

init – [in] container containing bytes to use as binary type

Returns:

JSON binary array value

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json binary (typename binary_t::container_type &&init, std::uint8_t subtype)

explicitly create a binary array (with subtype)

Creates a JSON binary array value from a given binary container. Binary values are part of various binary formats, such as CBOR, MessagePack, and BSON. This constructor is used to create a value for serialization to those formats.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

Since

version 3.8.0

Note

Note, this function exists because of the difficulty in correctly specifying the correct template overload in the standard value ctor, as both JSON arrays and JSON binary arrays are backed with some form of a std::vector. Because JSON binary arrays are a non-standard extension it was decided that it would be best to prevent automatic initialization of a binary array type, for backwards compatibility and so it does not happen on accident.

Parameters:

• init – [in] container containing bytes to use as binary type

• subtype – [in] subtype to use in MessagePack and BSON

Returns:

JSON binary array value

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json array (initializer_list_t init={})

explicitly create an array from an initializer list

Creates a JSON array value from a given initializer list. That is, given a list of values a, b, c, creates the JSON value [a, b, c]. If the initializer list is empty, the empty array [] is created.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows an example for the array function.,array}

See also

basic_json(initializer_list_t, bool, value_t) &#8212; create a JSON value from an initializer list

See also

object(initializer_list_t) &#8212; create a JSON object value from an initializer list

Since

version 1.0.0

Note

This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (basic_json(initializer_list_t, bool, value_t)). These cases are:

1. creating an array whose elements are all pairs whose first element is a string &#8212; in this case, the initializer list constructor would create an object, taking the first elements as keys

2. creating an empty array &#8212; passing the empty initializer list to the initializer list constructor yields an empty object

Parameters:

init – [in] initializer list with JSON values to create an array from (optional)

Returns:

JSON array value

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json object (initializer_list_t init={})

explicitly create an object from an initializer list

Creates a JSON object value from a given initializer list. The initializer lists elements must be pairs, and their first elements must be strings. If the initializer list is empty, the empty object {} is created.

@complexity Linear in the size of init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows an example for the object function.,object}

See also

basic_json(initializer_list_t, bool, value_t) &#8212; create a JSON value from an initializer list

See also

array(initializer_list_t) &#8212; create a JSON array value from an initializer list

Since

version 1.0.0

Note

This function is only added for symmetry reasons. In contrast to the related function array(initializer_list_t), there are no cases which can only be expressed by this function. That is, any initializer list init can also be passed to the initializer list constructor basic_json(initializer_list_t, bool, value_t).

Parameters:

init – [in] initializer list to create an object from (optional)

Throws:

type_error.301 – if init is not a list of pairs whose first elements are strings. In this case, no object can be created. When such a value is passed to basic_json(initializer_list_t, bool, value_t), an array would have been created from the passed initializer list init. See example below.

Returns:

JSON object value

inline basic_json(const value_t v)

create an empty value with a given type

Create an empty JSON value with a given type. The value will be default initialized with an empty value which depends on the type:

Value type	initial value
null	null
boolean	false
string	""
number	0
object	{}
array	[]

@complexity Constant.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows the constructor for different value_t values,basic_json__value_t}

See also

clear() &#8212; restores the postcondition of this constructor

Since

version 1.0.0

Parameters:

v – [in] the type of the value to create

inline basic_json(std::nullptr_t = nullptr) noexcept

create a null object

Create a null JSON value. It either takes a null pointer as parameter (explicitly creating null) or no parameter (implicitly creating null). The passed null pointer itself is not read &#8212; it is only used to choose the right constructor.

@complexity Constant.

@exceptionsafety No-throw guarantee: this constructor never throws exceptions.

@liveexample{The following code shows the constructor with and without a null pointer parameter.,basic_json__nullptr_t}

Since

version 1.0.0

template<typename CompatibleType, typename U = detail::uncvref_t<CompatibleType>, detail::enable_if_t<not detail::is_basic_json<U>::value and detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
inline basic_json(CompatibleType &&val) noexcept(noexcept(JSONSerializer<U>::to_json(std::declval<basic_json_t&>(), std::forward<CompatibleType>(val))))

create a JSON value

This is a “catch all” constructor for all compatible JSON types; that is, types for which a to_json() method exists. The constructor forwards the parameter val to that method (to json_serializer<U>::to_json method with U = uncvref_t<CompatibleType>, to be exact).

Template type CompatibleType includes, but is not limited to, the following types:

• arrays: array_t and all kinds of compatible containers such as std::vector, std::deque, std::list, std::forward_list, std::array, std::valarray, std::set, std::unordered_set, std::multiset, and std::unordered_multiset with a value_type from which a basic_json value can be constructed.

• objects: object_t and all kinds of compatible associative containers such as std::map, std::unordered_map, std::multimap, and std::unordered_multimap with a key_type compatible to string_t and a value_type from which a basic_json value can be constructed.

• strings: string_t, string literals, and all compatible string containers can be used.

• numbers: number_integer_t, number_unsigned_t, number_float_t, and all convertible number types such as int, size_t, int64_t, float or double can be used.

• boolean: boolean_t / bool can be used.

See the examples below.

@complexity Usually linear in the size of the passed val, also depending on the implementation of the called to_json() method.

Template Parameters:

• CompatibleType – a type such that:

  • CompatibleType is not derived from std::istream,

  • CompatibleType is not basic_json (to avoid hijacking copy/move constructors),

  • CompatibleType is not a different basic_json type (i.e. with different template arguments)

  • CompatibleType is not a basic_json nested type (e.g., json_pointer, iterator, etc …)

  • @ref json_serializer

• U –

Parameters:

val – [in]

template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value and not std::is_same<basic_json, BasicJsonType>::value, int> = 0>
inline basic_json(const BasicJsonType &val)

create a JSON value from an existing one

This is a constructor for existing basic_json types. It does not hijack copy/move constructors, since the parameter has different template arguments than the current ones.

The constructor tries to convert the internal m_value of the parameter.

@complexity Usually linear in the size of the passed val, also depending on the implementation of the called to_json() method.

@exceptionsafety Depends on the called constructor. For types directly supported by the library (i.e., all types for which no to_json() function was provided), strong guarantee holds: if an exception is thrown, there are no changes to any JSON value.

Since

version 3.2.0

Template Parameters:

BasicJsonType – a type such that:

• BasicJsonType is a basic_json type.

• BasicJsonType has different template arguments than basic_json_t.

Parameters:

val – [in] the basic_json value to be converted.

inline basic_json(initializer_list_t init, bool type_deduction = true, value_t manual_type = value_t::array)

create a container (array or object) from an initializer list

Creates a JSON value of type array or object from the passed initializer list init. In case type_deduction is true (default), the type of the JSON value to be created is deducted from the initializer list init according to the following rules:

1. If the list is empty, an empty JSON object value {} is created.

2. If the list consists of pairs whose first element is a string, a JSON object value is created where the first elements of the pairs are treated as keys and the second elements are as values.

3. In all other cases, an array is created.

The rules aim to create the best fit between a C++ initializer list and JSON values. The rationale is as follows:

1. The empty initializer list is written as {} which is exactly an empty JSON object.

2. C++ has no way of describing mapped types other than to list a list of pairs. As JSON requires that keys must be of type string, rule 2 is the weakest constraint one can pose on initializer lists to interpret them as an object.

3. In all other cases, the initializer list could not be interpreted as JSON object type, so interpreting it as JSON array type is safe.

With the rules described above, the following JSON values cannot be expressed by an initializer list:

• the empty array ([]): use array(initializer_list_t) with an empty initializer list in this case

• arrays whose elements satisfy rule 2: use array(initializer_list_t) with the same initializer list in this case

@complexity Linear in the size of the initializer list init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The example below shows how JSON values are created from initializer lists.,basic_json__list_init_t}

See also

array(initializer_list_t) &#8212; create a JSON array value from an initializer list

See also

object(initializer_list_t) &#8212; create a JSON object value from an initializer list

Since

version 1.0.0

Note

When used without parentheses around an empty initializer list, basic_json() is called instead of this function, yielding the JSON null value.

Parameters:

• init – [in] initializer list with JSON values

• type_deduction – [in] internal parameter; when set to true, the type of the JSON value is deducted from the initializer list init; when set to false, the type provided via manual_type is forced. This mode is used by the functions array(initializer_list_t) and object(initializer_list_t).

• manual_type – [in] internal parameter; when type_deduction is set to false, the created JSON value will use the provided type (only value_t::array and value_t::object are valid); when type_deduction is set to true, this parameter has no effect

Throws:

type_error.301 – if type_deduction is false, manual_type is value_t::object, but init contains an element which is not a pair whose first element is a string. In this case, the constructor could not create an object. If type_deduction would have be true, an array would have been created. See object(initializer_list_t) for an example.

inline basic_json(size_type cnt, const basic_json &val)

construct an array with count copies of given value

Constructs a JSON array value by creating cnt copies of a passed value. In case cnt is 0, an empty array is created.

@complexity Linear in cnt.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows examples for the basic_json(size_type\, const basic_json&) constructor.,basic_json__size_type_basic_json}

Since

version 1.0.0

Parameters:

• cnt – [in] the number of JSON copies of val to create

• val – [in] the JSON value to copy

Post:

std::distance(begin(),end()) == cnt holds.

template<class InputIT, typename std::enable_if<std::is_same<InputIT, typename basic_json_t::iterator>::value or std::is_same<InputIT, typename basic_json_t::const_iterator>::value, int>::type = 0>
inline basic_json(InputIT first, InputIT last)

construct a JSON container given an iterator range

Constructs the JSON value with the contents of the range [first, last). The semantics depends on the different types a JSON value can have:

• In case of a null type, invalid_iterator.206 is thrown.

• In case of other primitive types (number, boolean, or string), first must be begin() and last must be end(). In this case, the value is copied. Otherwise, invalid_iterator.204 is thrown.

• In case of structured types (array, object), the constructor behaves as similar versions for std::vector or std::map; that is, a JSON array or object is constructed from the values in the range.

@complexity Linear in distance between first and last.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The example below shows several ways to create JSON values by specifying a subrange with iterators.,basic_json__InputIt_InputIt}

Since

version 1.0.0

Warning

A precondition is enforced with a runtime assertion that will result in calling std::abort if this precondition is not met. Assertions can be disabled by defining NDEBUG at compile time. See https://en.cppreference.com/w/cpp/error/assert for more information.

Template Parameters:

InputIT – an input iterator type (iterator or const_iterator)

Parameters:

• first – [in] begin of the range to copy from (included)

• last – [in] end of the range to copy from (excluded)

Throws:

• invalid_iterator.201 – if iterators first and last are not compatible (i.e., do not belong to the same JSON value). In this case, the range [first, last) is undefined.

• invalid_iterator.204 – if iterators first and last belong to a primitive type (number, boolean, or string), but first does not point to the first element any more. In this case, the range [first, last) is undefined. See example code below.

• invalid_iterator.206 – if iterators first and last belong to a null value. In this case, the range [first, last) is undefined.

Pre:

Iterators first and last must be initialized. This precondition is enforced with an assertion (see warning). If assertions are switched off, a violation of this precondition yields undefined behavior.

Pre:

Range [first, last) is valid. Usually, this precondition cannot be checked efficiently. Only certain edge cases are detected; see the description of the exceptions below. A violation of this precondition yields undefined behavior.

inline basic_json(const basic_json &other)

copy constructor

Creates a copy of a given JSON value.

@complexity Linear in the size of other.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is linear.

• As postcondition, it holds: other == basic_json(other).

@liveexample{The following code shows an example for the copy constructor.,basic_json__basic_json}

Since

version 1.0.0

Parameters:

other – [in] the JSON value to copy

Post:

*this == other

inline basic_json(basic_json &&other) noexcept

move constructor

Move constructor. Constructs a JSON value with the contents of the given value other using move semantics. It “steals” the resources from other and leaves it as JSON null value.

@complexity Constant.

@exceptionsafety No-throw guarantee: this constructor never throws exceptions.

@requirement This function helps basic_json satisfying the MoveConstructible requirements.

@liveexample{The code below shows the move constructor explicitly called via std::move.,basic_json__moveconstructor}

Since

version 1.0.0

Parameters:

other – [inout] value to move to this object

Post:

*this has the same value as other before the call.

Post:

other is a JSON null value.

inline basic_json &operator=(basic_json other) noexcept(std::is_nothrow_move_constructible<value_t>::value and std::is_nothrow_move_assignable<value_t>::value and std::is_nothrow_move_constructible<json_value>::value and std::is_nothrow_move_assignable<json_value>::value)

copy assignment

Copy assignment operator. Copies a JSON value via the “copy and swap” strategy: It is expressed in terms of the copy constructor, destructor, and the swap() member function.

@complexity Linear.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is linear.

@liveexample{The code below shows and example for the copy assignment. It creates a copy of value a which is then swapped with b. Finally\, the copy of a (which is the null value after the swap) is destroyed.,basic_json__copyassignment}

Since

version 1.0.0

Parameters:

other – [in] value to copy from

inline ~basic_json() noexcept

destructor

Destroys the JSON value and frees all allocated memory.

@complexity Linear.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is linear.

• All stored elements are destroyed and all memory is freed.

Since

version 1.0.0

inline basic_json(const value_t v)

create an empty value with a given type

Create an empty JSON value with a given type. The value will be default initialized with an empty value which depends on the type:

Value type	initial value
null	null
boolean	false
string	""
number	0
object	{}
array	[]
binary	empty array

@complexity Constant.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows the constructor for different value_t values,basic_json__value_t}

See also

clear() &#8212; restores the postcondition of this constructor

Since

version 1.0.0

Parameters:

v – [in] the type of the value to create

inline basic_json(std::nullptr_t = nullptr) noexcept

create a null object

Create a null JSON value. It either takes a null pointer as parameter (explicitly creating null) or no parameter (implicitly creating null). The passed null pointer itself is not read &#8212; it is only used to choose the right constructor.

@complexity Constant.

@exceptionsafety No-throw guarantee: this constructor never throws exceptions.

@liveexample{The following code shows the constructor with and without a null pointer parameter.,basic_json__nullptr_t}

Since

version 1.0.0

template<typename CompatibleType, typename U = detail::uncvref_t<CompatibleType>, detail::enable_if_t<!detail::is_basic_json<U>::value && detail::is_compatible_type<basic_json_t, U>::value, int> = 0>
inline basic_json(CompatibleType &&val) noexcept(noexcept(JSONSerializer<U>::to_json(std::declval<basic_json_t&>(), std::forward<CompatibleType>(val))))

create a JSON value

This is a “catch all” constructor for all compatible JSON types; that is, types for which a to_json() method exists. The constructor forwards the parameter val to that method (to json_serializer<U>::to_json method with U = uncvref_t<CompatibleType>, to be exact).

Template type CompatibleType includes, but is not limited to, the following types:

• arrays: array_t and all kinds of compatible containers such as std::vector, std::deque, std::list, std::forward_list, std::array, std::valarray, std::set, std::unordered_set, std::multiset, and std::unordered_multiset with a value_type from which a basic_json value can be constructed.

• objects: object_t and all kinds of compatible associative containers such as std::map, std::unordered_map, std::multimap, and std::unordered_multimap with a key_type compatible to string_t and a value_type from which a basic_json value can be constructed.

• strings: string_t, string literals, and all compatible string containers can be used.

• numbers: number_integer_t, number_unsigned_t, number_float_t, and all convertible number types such as int, size_t, int64_t, float or double can be used.

• boolean: boolean_t / bool can be used.

• binary: binary_t / std::vector<uint8_t> may be used, unfortunately because string literals cannot be distinguished from binary character arrays by the C++ type system, all types compatible with const char* will be directed to the string constructor instead. This is both for backwards compatibility, and due to the fact that a binary type is not a standard JSON type.

See the examples below.

@complexity Usually linear in the size of the passed val, also depending on the implementation of the called to_json() method.

Template Parameters:

• CompatibleType – a type such that:

  • CompatibleType is not derived from std::istream,

  • CompatibleType is not basic_json (to avoid hijacking copy/move constructors),

  • CompatibleType is not a different basic_json type (i.e. with different template arguments)

  • CompatibleType is not a basic_json nested type (e.g., json_pointer, iterator, etc …)

  • @ref json_serializer

• U –

Parameters:

val – [in]

template<typename BasicJsonType, detail::enable_if_t<detail::is_basic_json<BasicJsonType>::value && !std::is_same<basic_json, BasicJsonType>::value, int> = 0>
inline basic_json(const BasicJsonType &val)

create a JSON value from an existing one

This is a constructor for existing basic_json types. It does not hijack copy/move constructors, since the parameter has different template arguments than the current ones.

The constructor tries to convert the internal m_value of the parameter.

@complexity Usually linear in the size of the passed val, also depending on the implementation of the called to_json() method.

@exceptionsafety Depends on the called constructor. For types directly supported by the library (i.e., all types for which no to_json() function was provided), strong guarantee holds: if an exception is thrown, there are no changes to any JSON value.

Since

version 3.2.0

Template Parameters:

BasicJsonType – a type such that:

• BasicJsonType is a basic_json type.

• BasicJsonType has different template arguments than basic_json_t.

Parameters:

val – [in] the basic_json value to be converted.

inline basic_json(initializer_list_t init, bool type_deduction = true, value_t manual_type = value_t::array)

create a container (array or object) from an initializer list

Creates a JSON value of type array or object from the passed initializer list init. In case type_deduction is true (default), the type of the JSON value to be created is deducted from the initializer list init according to the following rules:

1. If the list is empty, an empty JSON object value {} is created.

2. If the list consists of pairs whose first element is a string, a JSON object value is created where the first elements of the pairs are treated as keys and the second elements are as values.

3. In all other cases, an array is created.

The rules aim to create the best fit between a C++ initializer list and JSON values. The rationale is as follows:

1. The empty initializer list is written as {} which is exactly an empty JSON object.

2. C++ has no way of describing mapped types other than to list a list of pairs. As JSON requires that keys must be of type string, rule 2 is the weakest constraint one can pose on initializer lists to interpret them as an object.

3. In all other cases, the initializer list could not be interpreted as JSON object type, so interpreting it as JSON array type is safe.

With the rules described above, the following JSON values cannot be expressed by an initializer list:

• the empty array ([]): use array(initializer_list_t) with an empty initializer list in this case

• arrays whose elements satisfy rule 2: use array(initializer_list_t) with the same initializer list in this case

@complexity Linear in the size of the initializer list init.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The example below shows how JSON values are created from initializer lists.,basic_json__list_init_t}

See also

array(initializer_list_t) &#8212; create a JSON array value from an initializer list

See also

object(initializer_list_t) &#8212; create a JSON object value from an initializer list

Since

version 1.0.0

Note

When used without parentheses around an empty initializer list, basic_json() is called instead of this function, yielding the JSON null value.

Parameters:

• init – [in] initializer list with JSON values

• type_deduction – [in] internal parameter; when set to true, the type of the JSON value is deducted from the initializer list init; when set to false, the type provided via manual_type is forced. This mode is used by the functions array(initializer_list_t) and object(initializer_list_t).

• manual_type – [in] internal parameter; when type_deduction is set to false, the created JSON value will use the provided type (only value_t::array and value_t::object are valid); when type_deduction is set to true, this parameter has no effect

Throws:

type_error.301 – if type_deduction is false, manual_type is value_t::object, but init contains an element which is not a pair whose first element is a string. In this case, the constructor could not create an object. If type_deduction would have be true, an array would have been created. See object(initializer_list_t) for an example.

inline basic_json(size_type cnt, const basic_json &val)

construct an array with count copies of given value

Constructs a JSON array value by creating cnt copies of a passed value. In case cnt is 0, an empty array is created.

@complexity Linear in cnt.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The following code shows examples for the basic_json(size_type\, const basic_json&) constructor.,basic_json__size_type_basic_json}

Since

version 1.0.0

Parameters:

• cnt – [in] the number of JSON copies of val to create

• val – [in] the JSON value to copy

Post:

std::distance(begin(),end()) == cnt holds.

template<class InputIT, typename std::enable_if<std::is_same<InputIT, typename basic_json_t::iterator>::value || std::is_same<InputIT, typename basic_json_t::const_iterator>::value, int>::type = 0>
inline basic_json(InputIT first, InputIT last)

construct a JSON container given an iterator range

Constructs the JSON value with the contents of the range [first, last). The semantics depends on the different types a JSON value can have:

• In case of a null type, invalid_iterator.206 is thrown.

• In case of other primitive types (number, boolean, or string), first must be begin() and last must be end(). In this case, the value is copied. Otherwise, invalid_iterator.204 is thrown.

• In case of structured types (array, object), the constructor behaves as similar versions for std::vector or std::map; that is, a JSON array or object is constructed from the values in the range.

@complexity Linear in distance between first and last.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@liveexample{The example below shows several ways to create JSON values by specifying a subrange with iterators.,basic_json__InputIt_InputIt}

Since

version 1.0.0

Warning

A precondition is enforced with a runtime assertion that will result in calling std::abort if this precondition is not met. Assertions can be disabled by defining NDEBUG at compile time. See https://en.cppreference.com/w/cpp/error/assert for more information.

Template Parameters:

InputIT – an input iterator type (iterator or const_iterator)

Parameters:

• first – [in] begin of the range to copy from (included)

• last – [in] end of the range to copy from (excluded)

Throws:

• invalid_iterator.201 – if iterators first and last are not compatible (i.e., do not belong to the same JSON value). In this case, the range [first, last) is undefined.

• invalid_iterator.204 – if iterators first and last belong to a primitive type (number, boolean, or string), but first does not point to the first element any more. In this case, the range [first, last) is undefined. See example code below.

• invalid_iterator.206 – if iterators first and last belong to a null value. In this case, the range [first, last) is undefined.

Pre:

Iterators first and last must be initialized. This precondition is enforced with an assertion (see warning). If assertions are switched off, a violation of this precondition yields undefined behavior.

Pre:

Range [first, last) is valid. Usually, this precondition cannot be checked efficiently. Only certain edge cases are detected; see the description of the exceptions below. A violation of this precondition yields undefined behavior.

template<typename JsonRef, detail::enable_if_t<detail::conjunction<detail::is_json_ref<JsonRef>, std::is_same<typename JsonRef::value_type, basic_json>>::value, int> = 0>
inline basic_json(const JsonRef &ref)

inline basic_json(const basic_json &other)

copy constructor

Creates a copy of a given JSON value.

@complexity Linear in the size of other.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is linear.

• As postcondition, it holds: other == basic_json(other).

@liveexample{The following code shows an example for the copy constructor.,basic_json__basic_json}

Since

version 1.0.0

Parameters:

other – [in] the JSON value to copy

Post:

*this == other

inline basic_json(basic_json &&other) noexcept

move constructor

Move constructor. Constructs a JSON value with the contents of the given value other using move semantics. It “steals” the resources from other and leaves it as JSON null value.

@complexity Constant.

@exceptionsafety No-throw guarantee: this constructor never throws exceptions.

@requirement This function helps basic_json satisfying the MoveConstructible requirements.

@liveexample{The code below shows the move constructor explicitly called via std::move.,basic_json__moveconstructor}

Since

version 1.0.0

Parameters:

other – [inout] value to move to this object

Post:

*this has the same value as other before the call.

Post:

other is a JSON null value.

inline basic_json &operator=(basic_json other) noexcept(std::is_nothrow_move_constructible<value_t>::value && std::is_nothrow_move_assignable<value_t>::value && std::is_nothrow_move_constructible<json_value>::value && std::is_nothrow_move_assignable<json_value>::value)

copy assignment

Copy assignment operator. Copies a JSON value via the “copy and swap” strategy: It is expressed in terms of the copy constructor, destructor, and the swap() member function.

@complexity Linear.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is linear.

@liveexample{The code below shows and example for the copy assignment. It creates a copy of value a which is then swapped with b. Finally\, the copy of a (which is the null value after the swap) is destroyed.,basic_json__copyassignment}

Since

version 1.0.0

Parameters:

other – [in] value to copy from

inline ~basic_json() noexcept

destructor

Destroys the JSON value and frees all allocated memory.

@complexity Linear.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is linear.

• All stored elements are destroyed and all memory is freed.

Since

version 1.0.0

iterators

static inline iteration_proxy<iterator> iterator_wrapper(reference ref) noexcept

wrapper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without iterator_wrapper:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without iterator proxy:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with iterator proxy:

for (auto it : json::iterator_wrapper(j_object))
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

@liveexample{The following code shows how the wrapper is used,iterator_wrapper}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Deprecated:

This stream operator is deprecated and will be removed in future 4.0.0 of the library. Please use items() instead; that is, replace json::iterator_wrapper(j) with j.items().

Note

When iterating over an array, key() will return the index of the element as string (see example).

Note

The name of this function is not yet final and may change in the future.

Parameters:

ref – [in] reference to a JSON value

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

static inline iteration_proxy<const_iterator> iterator_wrapper(const_reference ref) noexcept

wrapper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without iterator_wrapper:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without iterator proxy:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with iterator proxy:

for (auto it : json::iterator_wrapper(j_object))
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

@liveexample{The following code shows how the wrapper is used,iterator_wrapper}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Deprecated:

This stream operator is deprecated and will be removed in future 4.0.0 of the library. Please use items() instead; that is, replace json::iterator_wrapper(j) with j.items().

Note

When iterating over an array, key() will return the index of the element as string (see example).

Note

The name of this function is not yet final and may change in the future.

Parameters:

ref – [in] reference to a JSON value

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

static inline iteration_proxy<iterator> iterator_wrapper(reference ref) noexcept

wrapper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without iterator_wrapper:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without iterator proxy:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with iterator proxy:

for (auto it : json::iterator_wrapper(j_object))
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

@liveexample{The following code shows how the wrapper is used,iterator_wrapper}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Deprecated:

This stream operator is deprecated and will be removed in future 4.0.0 of the library. Please use items() instead; that is, replace json::iterator_wrapper(j) with j.items().

Note

When iterating over an array, key() will return the index of the element as string (see example).

Note

The name of this function is not yet final and may change in the future.

Parameters:

ref – [in] reference to a JSON value

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

static inline iteration_proxy<const_iterator> iterator_wrapper(const_reference ref) noexcept

wrapper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without iterator_wrapper:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without iterator proxy:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with iterator proxy:

for (auto it : json::iterator_wrapper(j_object))
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

@liveexample{The following code shows how the wrapper is used,iterator_wrapper}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Deprecated:

This stream operator is deprecated and will be removed in future 4.0.0 of the library. Please use items() instead; that is, replace json::iterator_wrapper(j) with j.items().

Note

When iterating over an array, key() will return the index of the element as string (see example).

Note

The name of this function is not yet final and may change in the future.

Parameters:

ref – [in] reference to a JSON value

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

inline iterator begin() noexcept

returns an iterator to the first element

Returns an iterator to the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

@liveexample{The following code shows an example for begin().,begin}

See also

cbegin() &#8212; returns a const iterator to the beginning

See also

end() &#8212; returns an iterator to the end

See also

cend() &#8212; returns a const iterator to the end

Since

version 1.0.0

Returns:

iterator to the first element

inline const_iterator begin() const noexcept

returns a const iterator to the first element

Returns a const iterator to the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).begin().

@liveexample{The following code shows an example for cbegin().,cbegin}

See also

begin() &#8212; returns an iterator to the beginning

See also

end() &#8212; returns an iterator to the end

See also

cend() &#8212; returns a const iterator to the end

Since

version 1.0.0

Returns:

const iterator to the first element

inline const_iterator cbegin() const noexcept

returns a const iterator to the first element

Returns a const iterator to the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).begin().

@liveexample{The following code shows an example for cbegin().,cbegin}

See also

begin() &#8212; returns an iterator to the beginning

See also

end() &#8212; returns an iterator to the end

See also

cend() &#8212; returns a const iterator to the end

Since

version 1.0.0

Returns:

const iterator to the first element

inline iterator end() noexcept

returns an iterator to one past the last element

Returns an iterator to one past the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

@liveexample{The following code shows an example for end().,end}

See also

cend() &#8212; returns a const iterator to the end

See also

begin() &#8212; returns an iterator to the beginning

See also

cbegin() &#8212; returns a const iterator to the beginning

Since

version 1.0.0

Returns:

iterator one past the last element

inline const_iterator end() const noexcept

returns a const iterator to one past the last element

Returns a const iterator to one past the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).end().

@liveexample{The following code shows an example for cend().,cend}

See also

end() &#8212; returns an iterator to the end

See also

begin() &#8212; returns an iterator to the beginning

See also

cbegin() &#8212; returns a const iterator to the beginning

Since

version 1.0.0

Returns:

const iterator one past the last element

inline const_iterator cend() const noexcept

returns a const iterator to one past the last element

Returns a const iterator to one past the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).end().

@liveexample{The following code shows an example for cend().,cend}

See also

end() &#8212; returns an iterator to the end

See also

begin() &#8212; returns an iterator to the beginning

See also

cbegin() &#8212; returns a const iterator to the beginning

Since

version 1.0.0

Returns:

const iterator one past the last element

inline reverse_iterator rbegin() noexcept

returns an iterator to the reverse-beginning

Returns an iterator to the reverse-beginning; that is, the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of reverse_iterator(end()).

@liveexample{The following code shows an example for rbegin().,rbegin}

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

See also

rend() &#8212; returns a reverse iterator to the end

See also

crend() &#8212; returns a const reverse iterator to the end

Since

version 1.0.0

inline const_reverse_iterator rbegin() const noexcept

returns a const reverse iterator to the last element

Returns a const iterator to the reverse-beginning; that is, the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rbegin().

@liveexample{The following code shows an example for crbegin().,crbegin}

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

rend() &#8212; returns a reverse iterator to the end

See also

crend() &#8212; returns a const reverse iterator to the end

Since

version 1.0.0

inline reverse_iterator rend() noexcept

returns an iterator to the reverse-end

Returns an iterator to the reverse-end; that is, one before the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of reverse_iterator(begin()).

@liveexample{The following code shows an example for rend().,rend}

See also

crend() &#8212; returns a const reverse iterator to the end

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

Since

version 1.0.0

inline const_reverse_iterator rend() const noexcept

returns a const reverse iterator to one before the first

Returns a const reverse iterator to the reverse-end; that is, one before the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rend().

@liveexample{The following code shows an example for crend().,crend}

See also

rend() &#8212; returns a reverse iterator to the end

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

Since

version 1.0.0

inline const_reverse_iterator crbegin() const noexcept

returns a const reverse iterator to the last element

Returns a const iterator to the reverse-beginning; that is, the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rbegin().

@liveexample{The following code shows an example for crbegin().,crbegin}

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

rend() &#8212; returns a reverse iterator to the end

See also

crend() &#8212; returns a const reverse iterator to the end

Since

version 1.0.0

inline const_reverse_iterator crend() const noexcept

returns a const reverse iterator to one before the first

Returns a const reverse iterator to the reverse-end; that is, one before the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rend().

@liveexample{The following code shows an example for crend().,crend}

See also

rend() &#8212; returns a reverse iterator to the end

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

Since

version 1.0.0

inline iteration_proxy<iterator> items() noexcept

helper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without items() function:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without items() function:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with items() function:

for (auto& el : j_object.items())
{
    std::cout << "key: " << el.key() << ", value:" << el.value() << '\n';
}

The items() function also allows to use structured bindings (C++17):

for (auto& [key, val] : j_object.items())
{
    std::cout << "key: " << key << ", value:" << val << '\n';
}

@liveexample{The following code shows how the function is used.,items}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Since

version 3.1.0, structured bindings support since 3.5.0.

Note

When iterating over an array, key() will return the index of the element as string (see example). For primitive types (e.g., numbers), key() returns an empty string.

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

inline iteration_proxy<const_iterator> items() const noexcept

helper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without items() function:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without items() function:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with items() function:

for (auto& el : j_object.items())
{
    std::cout << "key: " << el.key() << ", value:" << el.value() << '\n';
}

The items() function also allows to use structured bindings (C++17):

for (auto& [key, val] : j_object.items())
{
    std::cout << "key: " << key << ", value:" << val << '\n';
}

@liveexample{The following code shows how the function is used.,items}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Since

version 3.1.0, structured bindings support since 3.5.0.

Note

When iterating over an array, key() will return the index of the element as string (see example). For primitive types (e.g., numbers), key() returns an empty string.

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

inline iterator begin() noexcept

returns an iterator to the first element

Returns an iterator to the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

@liveexample{The following code shows an example for begin().,begin}

See also

cbegin() &#8212; returns a const iterator to the beginning

See also

end() &#8212; returns an iterator to the end

See also

cend() &#8212; returns a const iterator to the end

Since

version 1.0.0

Returns:

iterator to the first element

inline const_iterator begin() const noexcept

returns a const iterator to the first element

Returns a const iterator to the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).begin().

@liveexample{The following code shows an example for cbegin().,cbegin}

See also

begin() &#8212; returns an iterator to the beginning

See also

end() &#8212; returns an iterator to the end

See also

cend() &#8212; returns a const iterator to the end

Since

version 1.0.0

Returns:

const iterator to the first element

inline const_iterator cbegin() const noexcept

returns a const iterator to the first element

Returns a const iterator to the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).begin().

@liveexample{The following code shows an example for cbegin().,cbegin}

See also

begin() &#8212; returns an iterator to the beginning

See also

end() &#8212; returns an iterator to the end

See also

cend() &#8212; returns a const iterator to the end

Since

version 1.0.0

Returns:

const iterator to the first element

inline iterator end() noexcept

returns an iterator to one past the last element

Returns an iterator to one past the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

@liveexample{The following code shows an example for end().,end}

See also

cend() &#8212; returns a const iterator to the end

See also

begin() &#8212; returns an iterator to the beginning

See also

cbegin() &#8212; returns a const iterator to the beginning

Since

version 1.0.0

Returns:

iterator one past the last element

inline const_iterator end() const noexcept

returns a const iterator to one past the last element

Returns a const iterator to one past the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).end().

@liveexample{The following code shows an example for cend().,cend}

See also

end() &#8212; returns an iterator to the end

See also

begin() &#8212; returns an iterator to the beginning

See also

cbegin() &#8212; returns a const iterator to the beginning

Since

version 1.0.0

Returns:

const iterator one past the last element

inline const_iterator cend() const noexcept

returns a const iterator to one past the last element

Returns a const iterator to one past the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).end().

@liveexample{The following code shows an example for cend().,cend}

See also

end() &#8212; returns an iterator to the end

See also

begin() &#8212; returns an iterator to the beginning

See also

cbegin() &#8212; returns a const iterator to the beginning

Since

version 1.0.0

Returns:

const iterator one past the last element

inline reverse_iterator rbegin() noexcept

returns an iterator to the reverse-beginning

Returns an iterator to the reverse-beginning; that is, the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of reverse_iterator(end()).

@liveexample{The following code shows an example for rbegin().,rbegin}

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

See also

rend() &#8212; returns a reverse iterator to the end

See also

crend() &#8212; returns a const reverse iterator to the end

Since

version 1.0.0

inline const_reverse_iterator rbegin() const noexcept

returns a const reverse iterator to the last element

Returns a const iterator to the reverse-beginning; that is, the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rbegin().

@liveexample{The following code shows an example for crbegin().,crbegin}

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

rend() &#8212; returns a reverse iterator to the end

See also

crend() &#8212; returns a const reverse iterator to the end

Since

version 1.0.0

inline reverse_iterator rend() noexcept

returns an iterator to the reverse-end

Returns an iterator to the reverse-end; that is, one before the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of reverse_iterator(begin()).

@liveexample{The following code shows an example for rend().,rend}

See also

crend() &#8212; returns a const reverse iterator to the end

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

Since

version 1.0.0

inline const_reverse_iterator rend() const noexcept

returns a const reverse iterator to one before the first

Returns a const reverse iterator to the reverse-end; that is, one before the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rend().

@liveexample{The following code shows an example for crend().,crend}

See also

rend() &#8212; returns a reverse iterator to the end

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

Since

version 1.0.0

inline const_reverse_iterator crbegin() const noexcept

returns a const reverse iterator to the last element

Returns a const iterator to the reverse-beginning; that is, the last element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rbegin().

@liveexample{The following code shows an example for crbegin().,crbegin}

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

rend() &#8212; returns a reverse iterator to the end

See also

crend() &#8212; returns a const reverse iterator to the end

Since

version 1.0.0

inline const_reverse_iterator crend() const noexcept

returns a const reverse iterator to one before the first

Returns a const reverse iterator to the reverse-end; that is, one before the first element.

@complexity Constant.

@requirement This function helps basic_json satisfying the ReversibleContainer requirements:

• The complexity is constant.

• Has the semantics of const_cast<const basic_json&>(*this).rend().

@liveexample{The following code shows an example for crend().,crend}

See also

rend() &#8212; returns a reverse iterator to the end

See also

rbegin() &#8212; returns a reverse iterator to the beginning

See also

crbegin() &#8212; returns a const reverse iterator to the beginning

Since

version 1.0.0

inline iteration_proxy<iterator> items() noexcept

helper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without items() function:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without items() function:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with items() function:

for (auto& el : j_object.items())
{
    std::cout << "key: " << el.key() << ", value:" << el.value() << '\n';
}

The items() function also allows to use structured bindings (C++17):

for (auto& [key, val] : j_object.items())
{
    std::cout << "key: " << key << ", value:" << val << '\n';
}

@liveexample{The following code shows how the function is used.,items}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Since

version 3.1.0, structured bindings support since 3.5.0.

Note

When iterating over an array, key() will return the index of the element as string (see example). For primitive types (e.g., numbers), key() returns an empty string.

Warning

Using items() on temporary objects is dangerous. Make sure the object’s lifetime exeeds the iteration. See https://github.com/nlohmann/json/issues/2040 for more information.

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

inline iteration_proxy<const_iterator> items() const noexcept

helper to access iterator member functions in range-based for

This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.

For loop without items() function:

for (auto it = j_object.begin(); it != j_object.end(); ++it)
{
    std::cout << "key: " << it.key() << ", value:" << it.value() << '\n';
}

Range-based for loop without items() function:

for (auto it : j_object)
{
    // "it" is of type json::reference and has no key() member
    std::cout << "value: " << it << '\n';
}

Range-based for loop with items() function:

for (auto& el : j_object.items())
{
    std::cout << "key: " << el.key() << ", value:" << el.value() << '\n';
}

The items() function also allows to use structured bindings (C++17):

for (auto& [key, val] : j_object.items())
{
    std::cout << "key: " << key << ", value:" << val << '\n';
}

@liveexample{The following code shows how the function is used.,items}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

Since

version 3.1.0, structured bindings support since 3.5.0.

Note

When iterating over an array, key() will return the index of the element as string (see example). For primitive types (e.g., numbers), key() returns an empty string.

Returns:

iteration proxy object wrapping ref with an interface to use in range-based for loops

binary serialization/deserialization support

static inline std::vector<uint8_t> to_cbor(const basic_json &j)

create a CBOR serialization of a given JSON value

Serializes a given JSON value j to a byte vector using the CBOR (Concise Binary Object Representation) serialization format. CBOR is a binary serialization format which aims to be more compact than JSON itself, yet more efficient to parse.

The library uses the following mapping from JSON values types to CBOR types according to the CBOR specification (RFC 7049):

JSON value type	value/range	CBOR type	first byte
null	null	Null	0xF6
boolean	true	True	0xF5
boolean	false	False	0xF4
number_integer	-9223372036854775808..-2147483649	Negative integer (8 bytes follow)	0x3B
number_integer	-2147483648..-32769	Negative integer (4 bytes follow)	0x3A
number_integer	-32768..-129	Negative integer (2 bytes follow)	0x39
number_integer	-128..-25	Negative integer (1 byte follow)	0x38
number_integer	-24..-1	Negative integer	0x20..0x37
number_integer	0..23	Integer	0x00..0x17
number_integer	24..255	Unsigned integer (1 byte follow)	0x18
number_integer	256..65535	Unsigned integer (2 bytes follow)	0x19
number_integer	65536..4294967295	Unsigned integer (4 bytes follow)	0x1A
number_integer	4294967296..18446744073709551615	Unsigned integer (8 bytes follow)	0x1B
number_unsigned	0..23	Integer	0x00..0x17
number_unsigned	24..255	Unsigned integer (1 byte follow)	0x18
number_unsigned	256..65535	Unsigned integer (2 bytes follow)	0x19
number_unsigned	65536..4294967295	Unsigned integer (4 bytes follow)	0x1A
number_unsigned	4294967296..18446744073709551615	Unsigned integer (8 bytes follow)	0x1B
number_float	any value	Double-Precision Float	0xFB
string	length: 0..23	UTF-8 string	0x60..0x77
string	length: 23..255	UTF-8 string (1 byte follow)	0x78
string	length: 256..65535	UTF-8 string (2 bytes follow)	0x79
string	length: 65536..4294967295	UTF-8 string (4 bytes follow)	0x7A
string	length: 4294967296..18446744073709551615	UTF-8 string (8 bytes follow)	0x7B
array	size: 0..23	array	0x80..0x97
array	size: 23..255	array (1 byte follow)	0x98
array	size: 256..65535	array (2 bytes follow)	0x99
array	size: 65536..4294967295	array (4 bytes follow)	0x9A
array	size: 4294967296..18446744073709551615	array (8 bytes follow)	0x9B
object	size: 0..23	map	0xA0..0xB7
object	size: 23..255	map (1 byte follow)	0xB8
object	size: 256..65535	map (2 bytes follow)	0xB9
object	size: 65536..4294967295	map (4 bytes follow)	0xBA
object	size: 4294967296..18446744073709551615	map (8 bytes follow)	0xBB

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in CBOR format.,to_cbor}

See also

http://cbor.io

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the analogous deserialization

See also

to_msgpack(const basic_json&) for the related MessagePack format

See also

to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format

Since

version 2.0.9

Note

The mapping is complete in the sense that any JSON value type can be converted to a CBOR value.

Note

If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the dump() function which serializes NaN or Infinity to null.

Note

The following CBOR types are not used in the conversion:

• byte strings (0x40..0x5F)

• UTF-8 strings terminated by “break” (0x7F)

• arrays terminated by “break” (0x9F)

• maps terminated by “break” (0xBF)

• date/time (0xC0..0xC1)

• bignum (0xC2..0xC3)

• decimal fraction (0xC4)

• bigfloat (0xC5)

• tagged items (0xC6..0xD4, 0xD8..0xDB)

• expected conversions (0xD5..0xD7)

• simple values (0xE0..0xF3, 0xF8)

• undefined (0xF7)

• half and single-precision floats (0xF9-0xFA)

• break (0xFF)

Parameters:

j – [in] JSON value to serialize

Returns:

MessagePack serialization as byte vector

static inline void to_cbor(const basic_json &j, detail::output_adapter<uint8_t> o)

static inline void to_cbor(const basic_json &j, detail::output_adapter<char> o)

static inline std::vector<uint8_t> to_msgpack(const basic_json &j)

create a MessagePack serialization of a given JSON value

Serializes a given JSON value j to a byte vector using the MessagePack serialization format. MessagePack is a binary serialization format which aims to be more compact than JSON itself, yet more efficient to parse.

The library uses the following mapping from JSON values types to MessagePack types according to the MessagePack specification:

JSON value type	value/range	MessagePack type	first byte
null	null	nil	0xC0
boolean	true	true	0xC3
boolean	false	false	0xC2
number_integer	-9223372036854775808..-2147483649	int64	0xD3
number_integer	-2147483648..-32769	int32	0xD2
number_integer	-32768..-129	int16	0xD1
number_integer	-128..-33	int8	0xD0
number_integer	-32..-1	negative fixint	0xE0..0xFF
number_integer	0..127	positive fixint	0x00..0x7F
number_integer	128..255	uint 8	0xCC
number_integer	256..65535	uint 16	0xCD
number_integer	65536..4294967295	uint 32	0xCE
number_integer	4294967296..18446744073709551615	uint 64	0xCF
number_unsigned	0..127	positive fixint	0x00..0x7F
number_unsigned	128..255	uint 8	0xCC
number_unsigned	256..65535	uint 16	0xCD
number_unsigned	65536..4294967295	uint 32	0xCE
number_unsigned	4294967296..18446744073709551615	uint 64	0xCF
number_float	any value	float 64	0xCB
string	length: 0..31	fixstr	0xA0..0xBF
string	length: 32..255	str 8	0xD9
string	length: 256..65535	str 16	0xDA
string	length: 65536..4294967295	str 32	0xDB
array	size: 0..15	fixarray	0x90..0x9F
array	size: 16..65535	array 16	0xDC
array	size: 65536..4294967295	array 32	0xDD
object	size: 0..15	fix map	0x80..0x8F
object	size: 16..65535	map 16	0xDE
object	size: 65536..4294967295	map 32	0xDF

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in MessagePack format.,to_msgpack}

See also

http://msgpack.org

See also

from_msgpack for the analogous deserialization

See also

to_cbor(const basic_json& for the related CBOR format

See also

to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format

Since

version 2.0.9

Note

The mapping is complete in the sense that any JSON value type can be converted to a MessagePack value.

Note

The following values can not be converted to a MessagePack value:

• strings with more than 4294967295 bytes

• arrays with more than 4294967295 elements

• objects with more than 4294967295 elements

Note

The following MessagePack types are not used in the conversion:

• bin 8 - bin 32 (0xC4..0xC6)

• ext 8 - ext 32 (0xC7..0xC9)

• float 32 (0xCA)

• fixext 1 - fixext 16 (0xD4..0xD8)

Note

Any MessagePack output created to_msgpack can be successfully parsed by from_msgpack.

Note

If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the dump() function which serializes NaN or Infinity to null.

Parameters:

j – [in] JSON value to serialize

Returns:

MessagePack serialization as byte vector

static inline void to_msgpack(const basic_json &j, detail::output_adapter<uint8_t> o)

static inline void to_msgpack(const basic_json &j, detail::output_adapter<char> o)

static inline std::vector<uint8_t> to_ubjson(const basic_json &j, const bool use_size = false, const bool use_type = false)

create a UBJSON serialization of a given JSON value

Serializes a given JSON value j to a byte vector using the UBJSON (Universal Binary JSON) serialization format. UBJSON aims to be more compact than JSON itself, yet more efficient to parse.

The library uses the following mapping from JSON values types to UBJSON types according to the UBJSON specification:

JSON value type	value/range	UBJSON type	marker
null	null	null	Z
boolean	true	true	T
boolean	false	false	F
number_integer	-9223372036854775808..-2147483649	int64	L
number_integer	-2147483648..-32769	int32	l
number_integer	-32768..-129	int16	I
number_integer	-128..127	int8	i
number_integer	128..255	uint8	U
number_integer	256..32767	int16	I
number_integer	32768..2147483647	int32	l
number_integer	2147483648..9223372036854775807	int64	L
number_unsigned	0..127	int8	i
number_unsigned	128..255	uint8	U
number_unsigned	256..32767	int16	I
number_unsigned	32768..2147483647	int32	l
number_unsigned	2147483648..9223372036854775807	int64	L
number_float	any value	float64	D
string	with shortest length indicator	string	S
array	see notes on optimized format	array	[
object	see notes on optimized format	map	{

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in UBJSON format.,to_ubjson}

See also

http://ubjson.org

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the analogous deserialization

See also

to_cbor(const basic_json& for the related CBOR format

See also

to_msgpack(const basic_json&) for the related MessagePack format

Since

version 3.1.0

Note

The mapping is complete in the sense that any JSON value type can be converted to a UBJSON value.

Note

The following values can not be converted to a UBJSON value:

• strings with more than 9223372036854775807 bytes (theoretical)

• unsigned integer numbers above 9223372036854775807

Note

The following markers are not used in the conversion:

• Z: no-op values are not created.

• C: single-byte strings are serialized with S markers.

Note

Any UBJSON output created to_ubjson can be successfully parsed by from_ubjson.

Note

If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the dump() function which serializes NaN or Infinity to null.

Note

The optimized formats for containers are supported: Parameter use_size adds size information to the beginning of a container and removes the closing marker. Parameter use_type further checks whether all elements of a container have the same type and adds the type marker to the beginning of the container. The use_type parameter must only be used together with use_size = true. Note that use_size = true alone may result in larger representations - the benefit of this parameter is that the receiving side is immediately informed on the number of elements of the container.

Parameters:

• j – [in] JSON value to serialize

• use_size – [in] whether to add size annotations to container types

• use_type – [in] whether to add type annotations to container types (must be combined with use_size = true)

Returns:

UBJSON serialization as byte vector

static inline void to_ubjson(const basic_json &j, detail::output_adapter<uint8_t> o, const bool use_size = false, const bool use_type = false)

static inline void to_ubjson(const basic_json &j, detail::output_adapter<char> o, const bool use_size = false, const bool use_type = false)

static inline std::vector<uint8_t> to_bson(const basic_json &j)

Serializes the given JSON object j to BSON and returns a vector containing the corresponding BSON-representation.

BSON (Binary JSON) is a binary format in which zero or more ordered key/value pairs are stored as a single entity (a so-called document).

The library uses the following mapping from JSON values types to BSON types:

JSON value type	value/range	BSON type	marker
null	null	null	0x0A
boolean	true, false	boolean	0x08
number_integer	-9223372036854775808..-2147483649	int64	0x12
number_integer	-2147483648..2147483647	int32	0x10
number_integer	2147483648..9223372036854775807	int64	0x12
number_unsigned	0..2147483647	int32	0x10
number_unsigned	2147483648..9223372036854775807	int64	0x12
number_unsigned	9223372036854775808..18446744073709551615	—	—
number_float	any value	double	0x01
string	any value	string	0x02
array	any value	document	0x04
object	any value	document	0x03

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in BSON format.,to_bson}

See also

http://bsonspec.org/spec.html

See also

from_bson(detail::input_adapter&&, const bool strict) for the analogous deserialization

See also

to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format

See also

to_cbor(const basic_json&) for the related CBOR format

See also

to_msgpack(const basic_json&) for the related MessagePack format

Note

Any BSON output created via to_bson can be successfully parsed by from_bson.

Warning

The mapping is incomplete, since only JSON-objects (and things contained therein) can be serialized to BSON. Also, integers larger than 9223372036854775807 cannot be serialized to BSON, and the keys may not contain U+0000, since they are serialized a zero-terminated c-strings.

Throws:

• out_of_range.407 – if j.is_number_unsigned() && j.get<std::uint64_t>() > 9223372036854775807

• out_of_range.409 – if a key in j contains a NULL (U+0000)

• type_error.317 – if !j.is_object()

Parameters:

j – [in] JSON value to serialize

Pre:

The input j is required to be an object: j.is_object() == true.

Returns:

BSON serialization as byte vector

static inline void to_bson(const basic_json &j, detail::output_adapter<uint8_t> o)

Serializes the given JSON object j to BSON and forwards the corresponding BSON-representation to the given output_adapter o.

See also

to_bson(const basic_json&)

Parameters:

• j – The JSON object to convert to BSON.

• o – The output adapter that receives the binary BSON representation.

Pre:

The input j shall be an object: j.is_object() == true

static inline void to_bson(const basic_json &j, detail::output_adapter<char> o)

Serializes the given JSON object j to BSON and forwards the corresponding BSON-representation to the given output_adapter o.

See also

to_bson(const basic_json&)

Parameters:

• j – The JSON object to convert to BSON.

• o – The output adapter that receives the binary BSON representation.

Pre:

The input j shall be an object: j.is_object() == true

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_cbor (detail::input_adapter &&i, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in CBOR format

Deserializes a given input i to a JSON value using the CBOR (Concise Binary Object Representation) serialization format.

The library maps CBOR types to JSON value types as follows:

CBOR type	JSON value type	first byte
Integer	number_unsigned	0x00..0x17
Unsigned integer	number_unsigned	0x18
Unsigned integer	number_unsigned	0x19
Unsigned integer	number_unsigned	0x1A
Unsigned integer	number_unsigned	0x1B
Negative integer	number_integer	0x20..0x37
Negative integer	number_integer	0x38
Negative integer	number_integer	0x39
Negative integer	number_integer	0x3A
Negative integer	number_integer	0x3B
Negative integer	number_integer	0x40..0x57
UTF-8 string	string	0x60..0x77
UTF-8 string	string	0x78
UTF-8 string	string	0x79
UTF-8 string	string	0x7A
UTF-8 string	string	0x7B
UTF-8 string	string	0x7F
array	array	0x80..0x97
array	array	0x98
array	array	0x99
array	array	0x9A
array	array	0x9B
array	array	0x9F
map	object	0xA0..0xB7
map	object	0xB8
map	object	0xB9
map	object	0xBA
map	object	0xBB
map	object	0xBF
False	false	0xF4
True	true	0xF5
Null	null	0xF6
Half-Precision Float	number_float	0xF9
Single-Precision Float	number_float	0xFA
Double-Precision Float	number_float	0xFB

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in CBOR format to a JSON value.,from_cbor}

See also

http://cbor.io

See also

to_cbor(const basic_json&) for the analogous serialization

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

Since

version 2.0.9; parameter start_index since 2.1.1; changed to consume input adapters, removed start_index parameter, and added strict parameter since 3.0.0; added allow_exceptions parameter since 3.2.0

Note

Any CBOR output created to_cbor can be successfully parsed by from_cbor.

Warning

The mapping is incomplete in the sense that not all CBOR types can be converted to a JSON value. The following CBOR types are not supported and will yield parse errors (parse_error.112):

• byte strings (0x40..0x5F)

• date/time (0xC0..0xC1)

• bignum (0xC2..0xC3)

• decimal fraction (0xC4)

• bigfloat (0xC5)

• tagged items (0xC6..0xD4, 0xD8..0xDB)

• expected conversions (0xD5..0xD7)

• simple values (0xE0..0xF3, 0xF8)

• undefined (0xF7)

Warning

CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps with keys other than UTF-8 strings are rejected (parse_error.113).

Parameters:

• i – [in] an input in CBOR format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if unsupported features from CBOR were used in the given input v or if the input is not valid CBOR

• parse_error.113 – if a string was expected as map key, but not found

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename A1, typename A2, detail::enable_if_t< std::is_constructible< detail::input_adapter, A1, A2 >::value, int > = 0> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_cbor (A1 &&a1, A2 &&a2, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in CBOR format

Deserializes a given input i to a JSON value using the CBOR (Concise Binary Object Representation) serialization format.

The library maps CBOR types to JSON value types as follows:

CBOR type	JSON value type	first byte
Integer	number_unsigned	0x00..0x17
Unsigned integer	number_unsigned	0x18
Unsigned integer	number_unsigned	0x19
Unsigned integer	number_unsigned	0x1A
Unsigned integer	number_unsigned	0x1B
Negative integer	number_integer	0x20..0x37
Negative integer	number_integer	0x38
Negative integer	number_integer	0x39
Negative integer	number_integer	0x3A
Negative integer	number_integer	0x3B
Negative integer	number_integer	0x40..0x57
UTF-8 string	string	0x60..0x77
UTF-8 string	string	0x78
UTF-8 string	string	0x79
UTF-8 string	string	0x7A
UTF-8 string	string	0x7B
UTF-8 string	string	0x7F
array	array	0x80..0x97
array	array	0x98
array	array	0x99
array	array	0x9A
array	array	0x9B
array	array	0x9F
map	object	0xA0..0xB7
map	object	0xB8
map	object	0xB9
map	object	0xBA
map	object	0xBB
map	object	0xBF
False	false	0xF4
True	true	0xF5
Null	null	0xF6
Half-Precision Float	number_float	0xF9
Single-Precision Float	number_float	0xFA
Double-Precision Float	number_float	0xFB

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in CBOR format to a JSON value.,from_cbor}

See also

http://cbor.io

See also

to_cbor(const basic_json&) for the analogous serialization

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

Since

version 2.0.9; parameter start_index since 2.1.1; changed to consume input adapters, removed start_index parameter, and added strict parameter since 3.0.0; added allow_exceptions parameter since 3.2.0

Note

Any CBOR output created to_cbor can be successfully parsed by from_cbor.

Warning

The mapping is incomplete in the sense that not all CBOR types can be converted to a JSON value. The following CBOR types are not supported and will yield parse errors (parse_error.112):

• byte strings (0x40..0x5F)

• date/time (0xC0..0xC1)

• bignum (0xC2..0xC3)

• decimal fraction (0xC4)

• bigfloat (0xC5)

• tagged items (0xC6..0xD4, 0xD8..0xDB)

• expected conversions (0xD5..0xD7)

• simple values (0xE0..0xF3, 0xF8)

• undefined (0xF7)

Warning

CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps with keys other than UTF-8 strings are rejected (parse_error.113).

Parameters:

• i – [in] an input in CBOR format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if unsupported features from CBOR were used in the given input v or if the input is not valid CBOR

• parse_error.113 – if a string was expected as map key, but not found

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_msgpack (detail::input_adapter &&i, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in MessagePack format

Deserializes a given input i to a JSON value using the MessagePack serialization format.

The library maps MessagePack types to JSON value types as follows:

MessagePack type	JSON value type	first byte
positive fixint	number_unsigned	0x00..0x7F
fixmap	object	0x80..0x8F
fixarray	array	0x90..0x9F
fixstr	string	0xA0..0xBF
nil	null	0xC0
false	false	0xC2
true	true	0xC3
float 32	number_float	0xCA
float 64	number_float	0xCB
uint 8	number_unsigned	0xCC
uint 16	number_unsigned	0xCD
uint 32	number_unsigned	0xCE
uint 64	number_unsigned	0xCF
int 8	number_integer	0xD0
int 16	number_integer	0xD1
int 32	number_integer	0xD2
int 64	number_integer	0xD3
str 8	string	0xD9
str 16	string	0xDA
str 32	string	0xDB
array 16	array	0xDC
array 32	array	0xDD
map 16	object	0xDE
map 32	object	0xDF
negative fixint	number_integer	0xE0-0xFF

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in MessagePack format to a JSON value.,from_msgpack}

See also

http://msgpack.org

See also

to_msgpack(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 2.0.9; parameter start_index since 2.1.1; changed to consume input adapters, removed start_index parameter, and added strict parameter since 3.0.0; added allow_exceptions parameter since 3.2.0

Note

Any MessagePack output created to_msgpack can be successfully parsed by from_msgpack.

Warning

The mapping is incomplete in the sense that not all MessagePack types can be converted to a JSON value. The following MessagePack types are not supported and will yield parse errors:

• bin 8 - bin 32 (0xC4..0xC6)

• ext 8 - ext 32 (0xC7..0xC9)

• fixext 1 - fixext 16 (0xD4..0xD8)

Parameters:

• i – [in] an input in MessagePack format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if unsupported features from MessagePack were used in the given input i or if the input is not valid MessagePack

• parse_error.113 – if a string was expected as map key, but not found

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename A1, typename A2, detail::enable_if_t< std::is_constructible< detail::input_adapter, A1, A2 >::value, int > = 0> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_msgpack (A1 &&a1, A2 &&a2, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in MessagePack format

Deserializes a given input i to a JSON value using the MessagePack serialization format.

The library maps MessagePack types to JSON value types as follows:

MessagePack type	JSON value type	first byte
positive fixint	number_unsigned	0x00..0x7F
fixmap	object	0x80..0x8F
fixarray	array	0x90..0x9F
fixstr	string	0xA0..0xBF
nil	null	0xC0
false	false	0xC2
true	true	0xC3
float 32	number_float	0xCA
float 64	number_float	0xCB
uint 8	number_unsigned	0xCC
uint 16	number_unsigned	0xCD
uint 32	number_unsigned	0xCE
uint 64	number_unsigned	0xCF
int 8	number_integer	0xD0
int 16	number_integer	0xD1
int 32	number_integer	0xD2
int 64	number_integer	0xD3
str 8	string	0xD9
str 16	string	0xDA
str 32	string	0xDB
array 16	array	0xDC
array 32	array	0xDD
map 16	object	0xDE
map 32	object	0xDF
negative fixint	number_integer	0xE0-0xFF

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in MessagePack format to a JSON value.,from_msgpack}

See also

http://msgpack.org

See also

to_msgpack(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 2.0.9; parameter start_index since 2.1.1; changed to consume input adapters, removed start_index parameter, and added strict parameter since 3.0.0; added allow_exceptions parameter since 3.2.0

Note

Any MessagePack output created to_msgpack can be successfully parsed by from_msgpack.

Warning

The mapping is incomplete in the sense that not all MessagePack types can be converted to a JSON value. The following MessagePack types are not supported and will yield parse errors:

• bin 8 - bin 32 (0xC4..0xC6)

• ext 8 - ext 32 (0xC7..0xC9)

• fixext 1 - fixext 16 (0xD4..0xD8)

Parameters:

• i – [in] an input in MessagePack format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if unsupported features from MessagePack were used in the given input i or if the input is not valid MessagePack

• parse_error.113 – if a string was expected as map key, but not found

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_ubjson (detail::input_adapter &&i, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in UBJSON format

Deserializes a given input i to a JSON value using the UBJSON (Universal Binary JSON) serialization format.

The library maps UBJSON types to JSON value types as follows:

UBJSON type	JSON value type	marker
no-op	no value, next value is read	N
null	null	Z
false	false	F
true	true	T
float32	number_float	d
float64	number_float	D
uint8	number_unsigned	U
int8	number_integer	i
int16	number_integer	I
int32	number_integer	l
int64	number_integer	L
string	string	S
char	string	C
array	array (optimized values are supported)	[
object	object (optimized values are supported)	{

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in UBJSON format to a JSON value.,from_ubjson}

See also

http://ubjson.org

See also

to_ubjson(const basic_json&, const bool, const bool) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 3.1.0; added allow_exceptions parameter since 3.2.0

Note

The mapping is complete in the sense that any UBJSON value can be converted to a JSON value.

Parameters:

• i – [in] an input in UBJSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if a parse error occurs

• parse_error.113 – if a string could not be parsed successfully

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename A1, typename A2, detail::enable_if_t< std::is_constructible< detail::input_adapter, A1, A2 >::value, int > = 0> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_ubjson (A1 &&a1, A2 &&a2, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in UBJSON format

Deserializes a given input i to a JSON value using the UBJSON (Universal Binary JSON) serialization format.

The library maps UBJSON types to JSON value types as follows:

UBJSON type	JSON value type	marker
no-op	no value, next value is read	N
null	null	Z
false	false	F
true	true	T
float32	number_float	d
float64	number_float	D
uint8	number_unsigned	U
int8	number_integer	i
int16	number_integer	I
int32	number_integer	l
int64	number_integer	L
string	string	S
char	string	C
array	array (optimized values are supported)	[
object	object (optimized values are supported)	{

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in UBJSON format to a JSON value.,from_ubjson}

See also

http://ubjson.org

See also

to_ubjson(const basic_json&, const bool, const bool) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 3.1.0; added allow_exceptions parameter since 3.2.0

Note

The mapping is complete in the sense that any UBJSON value can be converted to a JSON value.

Parameters:

• i – [in] an input in UBJSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if a parse error occurs

• parse_error.113 – if a string could not be parsed successfully

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_bson (detail::input_adapter &&i, const bool strict=true, const bool allow_exceptions=true)

Create a JSON value from an input in BSON format.

Deserializes a given input i to a JSON value using the BSON (Binary JSON) serialization format.

The library maps BSON record types to JSON value types as follows:

BSON type	BSON marker byte	JSON value type
double	0x01	number_float
string	0x02	string
document	0x03	object
array	0x04	array
binary	0x05	still unsupported
undefined	0x06	still unsupported
ObjectId	0x07	still unsupported
boolean	0x08	boolean
UTC Date-Time	0x09	still unsupported
null	0x0A	null
Regular Expr.	0x0B	still unsupported
DB Pointer	0x0C	still unsupported
JavaScript Code	0x0D	still unsupported
Symbol	0x0E	still unsupported
JavaScript Code	0x0F	still unsupported
int32	0x10	number_integer
Timestamp	0x11	still unsupported
128-bit decimal float	0x13	still unsupported
Max Key	0x7F	still unsupported
Min Key	0xFF	still unsupported

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in BSON format to a JSON value.,from_bson}

See also

http://bsonspec.org/spec.html

See also

to_bson(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

Warning

The mapping is incomplete. The unsupported mappings are indicated in the table above.

Parameters:

• i – [in] an input in BSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

parse_error.114 – if an unsupported BSON record type is encountered

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename A1, typename A2, detail::enable_if_t< std::is_constructible< detail::input_adapter, A1, A2 >::value, int > = 0> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_bson (A1 &&a1, A2 &&a2, const bool strict=true, const bool allow_exceptions=true)

Create a JSON value from an input in BSON format.

Deserializes a given input i to a JSON value using the BSON (Binary JSON) serialization format.

The library maps BSON record types to JSON value types as follows:

BSON type	BSON marker byte	JSON value type
double	0x01	number_float
string	0x02	string
document	0x03	object
array	0x04	array
binary	0x05	still unsupported
undefined	0x06	still unsupported
ObjectId	0x07	still unsupported
boolean	0x08	boolean
UTC Date-Time	0x09	still unsupported
null	0x0A	null
Regular Expr.	0x0B	still unsupported
DB Pointer	0x0C	still unsupported
JavaScript Code	0x0D	still unsupported
Symbol	0x0E	still unsupported
JavaScript Code	0x0F	still unsupported
int32	0x10	number_integer
Timestamp	0x11	still unsupported
128-bit decimal float	0x13	still unsupported
Max Key	0x7F	still unsupported
Min Key	0xFF	still unsupported

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in BSON format to a JSON value.,from_bson}

See also

http://bsonspec.org/spec.html

See also

to_bson(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

Warning

The mapping is incomplete. The unsupported mappings are indicated in the table above.

Parameters:

• i – [in] an input in BSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

parse_error.114 – if an unsupported BSON record type is encountered

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

static inline std::vector<uint8_t> to_cbor(const basic_json &j)

create a CBOR serialization of a given JSON value

Serializes a given JSON value j to a byte vector using the CBOR (Concise Binary Object Representation) serialization format. CBOR is a binary serialization format which aims to be more compact than JSON itself, yet more efficient to parse.

The library uses the following mapping from JSON values types to CBOR types according to the CBOR specification (RFC 7049):

JSON value type	value/range	CBOR type	first byte
null	null	Null	0xF6
boolean	true	True	0xF5
boolean	false	False	0xF4
number_integer	-9223372036854775808..-2147483649	Negative integer (8 bytes follow)	0x3B
number_integer	-2147483648..-32769	Negative integer (4 bytes follow)	0x3A
number_integer	-32768..-129	Negative integer (2 bytes follow)	0x39
number_integer	-128..-25	Negative integer (1 byte follow)	0x38
number_integer	-24..-1	Negative integer	0x20..0x37
number_integer	0..23	Integer	0x00..0x17
number_integer	24..255	Unsigned integer (1 byte follow)	0x18
number_integer	256..65535	Unsigned integer (2 bytes follow)	0x19
number_integer	65536..4294967295	Unsigned integer (4 bytes follow)	0x1A
number_integer	4294967296..18446744073709551615	Unsigned integer (8 bytes follow)	0x1B
number_unsigned	0..23	Integer	0x00..0x17
number_unsigned	24..255	Unsigned integer (1 byte follow)	0x18
number_unsigned	256..65535	Unsigned integer (2 bytes follow)	0x19
number_unsigned	65536..4294967295	Unsigned integer (4 bytes follow)	0x1A
number_unsigned	4294967296..18446744073709551615	Unsigned integer (8 bytes follow)	0x1B
number_float	any value representable by a float	Single-Precision Float	0xFA
number_float	any value NOT representable by a float	Double-Precision Float	0xFB
string	length: 0..23	UTF-8 string	0x60..0x77
string	length: 23..255	UTF-8 string (1 byte follow)	0x78
string	length: 256..65535	UTF-8 string (2 bytes follow)	0x79
string	length: 65536..4294967295	UTF-8 string (4 bytes follow)	0x7A
string	length: 4294967296..18446744073709551615	UTF-8 string (8 bytes follow)	0x7B
array	size: 0..23	array	0x80..0x97
array	size: 23..255	array (1 byte follow)	0x98
array	size: 256..65535	array (2 bytes follow)	0x99
array	size: 65536..4294967295	array (4 bytes follow)	0x9A
array	size: 4294967296..18446744073709551615	array (8 bytes follow)	0x9B
object	size: 0..23	map	0xA0..0xB7
object	size: 23..255	map (1 byte follow)	0xB8
object	size: 256..65535	map (2 bytes follow)	0xB9
object	size: 65536..4294967295	map (4 bytes follow)	0xBA
object	size: 4294967296..18446744073709551615	map (8 bytes follow)	0xBB
binary	size: 0..23	byte string	0x40..0x57
binary	size: 23..255	byte string (1 byte follow)	0x58
binary	size: 256..65535	byte string (2 bytes follow)	0x59
binary	size: 65536..4294967295	byte string (4 bytes follow)	0x5A
binary	size: 4294967296..18446744073709551615	byte string (8 bytes follow)	0x5B

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in CBOR format.,to_cbor}

See also

http://cbor.io

See also

from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the analogous deserialization

See also

to_msgpack(const basic_json&) for the related MessagePack format

See also

to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format

Since

version 2.0.9; compact representation of floating-point numbers since version 3.8.0

Note

The mapping is complete in the sense that any JSON value type can be converted to a CBOR value.

Note

If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the dump() function which serializes NaN or Infinity to null.

Note

The following CBOR types are not used in the conversion:

• UTF-8 strings terminated by “break” (0x7F)

• arrays terminated by “break” (0x9F)

• maps terminated by “break” (0xBF)

• byte strings terminated by “break” (0x5F)

• date/time (0xC0..0xC1)

• bignum (0xC2..0xC3)

• decimal fraction (0xC4)

• bigfloat (0xC5)

• expected conversions (0xD5..0xD7)

• simple values (0xE0..0xF3, 0xF8)

• undefined (0xF7)

• half-precision floats (0xF9)

• break (0xFF)

Parameters:

j – [in] JSON value to serialize

Returns:

CBOR serialization as byte vector

static inline void to_cbor(const basic_json &j, detail::output_adapter<uint8_t> o)

static inline void to_cbor(const basic_json &j, detail::output_adapter<char> o)

static inline std::vector<uint8_t> to_msgpack(const basic_json &j)

create a MessagePack serialization of a given JSON value

Serializes a given JSON value j to a byte vector using the MessagePack serialization format. MessagePack is a binary serialization format which aims to be more compact than JSON itself, yet more efficient to parse.

The library uses the following mapping from JSON values types to MessagePack types according to the MessagePack specification:

JSON value type	value/range	MessagePack type	first byte
null	null	nil	0xC0
boolean	true	true	0xC3
boolean	false	false	0xC2
number_integer	-9223372036854775808..-2147483649	int64	0xD3
number_integer	-2147483648..-32769	int32	0xD2
number_integer	-32768..-129	int16	0xD1
number_integer	-128..-33	int8	0xD0
number_integer	-32..-1	negative fixint	0xE0..0xFF
number_integer	0..127	positive fixint	0x00..0x7F
number_integer	128..255	uint 8	0xCC
number_integer	256..65535	uint 16	0xCD
number_integer	65536..4294967295	uint 32	0xCE
number_integer	4294967296..18446744073709551615	uint 64	0xCF
number_unsigned	0..127	positive fixint	0x00..0x7F
number_unsigned	128..255	uint 8	0xCC
number_unsigned	256..65535	uint 16	0xCD
number_unsigned	65536..4294967295	uint 32	0xCE
number_unsigned	4294967296..18446744073709551615	uint 64	0xCF
number_float	any value representable by a float	float 32	0xCA
number_float	any value NOT representable by a float	float 64	0xCB
string	length: 0..31	fixstr	0xA0..0xBF
string	length: 32..255	str 8	0xD9
string	length: 256..65535	str 16	0xDA
string	length: 65536..4294967295	str 32	0xDB
array	size: 0..15	fixarray	0x90..0x9F
array	size: 16..65535	array 16	0xDC
array	size: 65536..4294967295	array 32	0xDD
object	size: 0..15	fix map	0x80..0x8F
object	size: 16..65535	map 16	0xDE
object	size: 65536..4294967295	map 32	0xDF
binary	size: 0..255	bin 8	0xC4
binary	size: 256..65535	bin 16	0xC5
binary	size: 65536..4294967295	bin 32	0xC6

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in MessagePack format.,to_msgpack}

See also

http://msgpack.org

See also

from_msgpack for the analogous deserialization

See also

to_cbor(const basic_json& for the related CBOR format

See also

to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format

Since

version 2.0.9

Note

The mapping is complete in the sense that any JSON value type can be converted to a MessagePack value.

Note

The following values can not be converted to a MessagePack value:

• strings with more than 4294967295 bytes

• byte strings with more than 4294967295 bytes

• arrays with more than 4294967295 elements

• objects with more than 4294967295 elements

Note

Any MessagePack output created to_msgpack can be successfully parsed by from_msgpack.

Note

If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the dump() function which serializes NaN or Infinity to null.

Parameters:

j – [in] JSON value to serialize

Returns:

MessagePack serialization as byte vector

static inline void to_msgpack(const basic_json &j, detail::output_adapter<uint8_t> o)

static inline void to_msgpack(const basic_json &j, detail::output_adapter<char> o)

static inline std::vector<uint8_t> to_ubjson(const basic_json &j, const bool use_size = false, const bool use_type = false)

create a UBJSON serialization of a given JSON value

Serializes a given JSON value j to a byte vector using the UBJSON (Universal Binary JSON) serialization format. UBJSON aims to be more compact than JSON itself, yet more efficient to parse.

The library uses the following mapping from JSON values types to UBJSON types according to the UBJSON specification:

JSON value type	value/range	UBJSON type	marker
null	null	null	Z
boolean	true	true	T
boolean	false	false	F
number_integer	-9223372036854775808..-2147483649	int64	L
number_integer	-2147483648..-32769	int32	l
number_integer	-32768..-129	int16	I
number_integer	-128..127	int8	i
number_integer	128..255	uint8	U
number_integer	256..32767	int16	I
number_integer	32768..2147483647	int32	l
number_integer	2147483648..9223372036854775807	int64	L
number_unsigned	0..127	int8	i
number_unsigned	128..255	uint8	U
number_unsigned	256..32767	int16	I
number_unsigned	32768..2147483647	int32	l
number_unsigned	2147483648..9223372036854775807	int64	L
number_unsigned	2147483649..18446744073709551615	high-precision	H
number_float	any value	float64	D
string	with shortest length indicator	string	S
array	see notes on optimized format	array	[
object	see notes on optimized format	map	{

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in UBJSON format.,to_ubjson}

See also

http://ubjson.org

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the analogous deserialization

See also

to_cbor(const basic_json& for the related CBOR format

See also

to_msgpack(const basic_json&) for the related MessagePack format

Since

version 3.1.0

Note

The mapping is complete in the sense that any JSON value type can be converted to a UBJSON value.

Note

The following values can not be converted to a UBJSON value:

• strings with more than 9223372036854775807 bytes (theoretical)

Note

The following markers are not used in the conversion:

• Z: no-op values are not created.

• C: single-byte strings are serialized with S markers.

Note

Any UBJSON output created to_ubjson can be successfully parsed by from_ubjson.

Note

If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the dump() function which serializes NaN or Infinity to null.

Note

The optimized formats for containers are supported: Parameter use_size adds size information to the beginning of a container and removes the closing marker. Parameter use_type further checks whether all elements of a container have the same type and adds the type marker to the beginning of the container. The use_type parameter must only be used together with use_size = true. Note that use_size = true alone may result in larger representations - the benefit of this parameter is that the receiving side is immediately informed on the number of elements of the container.

Note

If the JSON data contains the binary type, the value stored is a list of integers, as suggested by the UBJSON documentation. In particular, this means that serialization and the deserialization of a JSON containing binary values into UBJSON and back will result in a different JSON object.

Parameters:

• j – [in] JSON value to serialize

• use_size – [in] whether to add size annotations to container types

• use_type – [in] whether to add type annotations to container types (must be combined with use_size = true)

Returns:

UBJSON serialization as byte vector

static inline void to_ubjson(const basic_json &j, detail::output_adapter<uint8_t> o, const bool use_size = false, const bool use_type = false)

static inline void to_ubjson(const basic_json &j, detail::output_adapter<char> o, const bool use_size = false, const bool use_type = false)

static inline std::vector<uint8_t> to_bson(const basic_json &j)

Serializes the given JSON object j to BSON and returns a vector containing the corresponding BSON-representation.

BSON (Binary JSON) is a binary format in which zero or more ordered key/value pairs are stored as a single entity (a so-called document).

The library uses the following mapping from JSON values types to BSON types:

JSON value type	value/range	BSON type	marker
null	null	null	0x0A
boolean	true, false	boolean	0x08
number_integer	-9223372036854775808..-2147483649	int64	0x12
number_integer	-2147483648..2147483647	int32	0x10
number_integer	2147483648..9223372036854775807	int64	0x12
number_unsigned	0..2147483647	int32	0x10
number_unsigned	2147483648..9223372036854775807	int64	0x12
number_unsigned	9223372036854775808..18446744073709551615	—	—
number_float	any value	double	0x01
string	any value	string	0x02
array	any value	document	0x04
object	any value	document	0x03
binary	any value	binary	0x05

@complexity Linear in the size of the JSON value j.

@liveexample{The example shows the serialization of a JSON value to a byte vector in BSON format.,to_bson}

See also

http://bsonspec.org/spec.html

See also

from_bson(detail::input_adapter&&, const bool strict) for the analogous deserialization

See also

to_ubjson(const basic_json&, const bool, const bool) for the related UBJSON format

See also

to_cbor(const basic_json&) for the related CBOR format

See also

to_msgpack(const basic_json&) for the related MessagePack format

Note

Any BSON output created via to_bson can be successfully parsed by from_bson.

Warning

The mapping is incomplete, since only JSON-objects (and things contained therein) can be serialized to BSON. Also, integers larger than 9223372036854775807 cannot be serialized to BSON, and the keys may not contain U+0000, since they are serialized a zero-terminated c-strings.

Throws:

• out_of_range.407 – if j.is_number_unsigned() && j.get<std::uint64_t>() > 9223372036854775807

• out_of_range.409 – if a key in j contains a NULL (U+0000)

• type_error.317 – if !j.is_object()

Parameters:

j – [in] JSON value to serialize

Pre:

The input j is required to be an object: j.is_object() == true.

Returns:

BSON serialization as byte vector

static inline void to_bson(const basic_json &j, detail::output_adapter<uint8_t> o)

Serializes the given JSON object j to BSON and forwards the corresponding BSON-representation to the given output_adapter o.

See also

to_bson(const basic_json&)

Parameters:

• j – The JSON object to convert to BSON.

• o – The output adapter that receives the binary BSON representation.

Pre:

The input j shall be an object: j.is_object() == true

static inline void to_bson(const basic_json &j, detail::output_adapter<char> o)

Serializes the given JSON object j to BSON and forwards the corresponding BSON-representation to the given output_adapter o.

See also

to_bson(const basic_json&)

Parameters:

• j – The JSON object to convert to BSON.

• o – The output adapter that receives the binary BSON representation.

Pre:

The input j shall be an object: j.is_object() == true

template<typename InputType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_cbor (InputType &&i, const bool strict=true, const bool allow_exceptions=true, const cbor_tag_handler_t tag_handler=cbor_tag_handler_t::error)

create a JSON value from an input in CBOR format

Deserializes a given input i to a JSON value using the CBOR (Concise Binary Object Representation) serialization format.

The library maps CBOR types to JSON value types as follows:

CBOR type	JSON value type	first byte
Integer	number_unsigned	0x00..0x17
Unsigned integer	number_unsigned	0x18
Unsigned integer	number_unsigned	0x19
Unsigned integer	number_unsigned	0x1A
Unsigned integer	number_unsigned	0x1B
Negative integer	number_integer	0x20..0x37
Negative integer	number_integer	0x38
Negative integer	number_integer	0x39
Negative integer	number_integer	0x3A
Negative integer	number_integer	0x3B
Byte string	binary	0x40..0x57
Byte string	binary	0x58
Byte string	binary	0x59
Byte string	binary	0x5A
Byte string	binary	0x5B
UTF-8 string	string	0x60..0x77
UTF-8 string	string	0x78
UTF-8 string	string	0x79
UTF-8 string	string	0x7A
UTF-8 string	string	0x7B
UTF-8 string	string	0x7F
array	array	0x80..0x97
array	array	0x98
array	array	0x99
array	array	0x9A
array	array	0x9B
array	array	0x9F
map	object	0xA0..0xB7
map	object	0xB8
map	object	0xB9
map	object	0xBA
map	object	0xBB
map	object	0xBF
False	false	0xF4
True	true	0xF5
Null	null	0xF6
Half-Precision Float	number_float	0xF9
Single-Precision Float	number_float	0xFA
Double-Precision Float	number_float	0xFB

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in CBOR format to a JSON value.,from_cbor}

See also

http://cbor.io

See also

to_cbor(const basic_json&) for the analogous serialization

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

Since

version 2.0.9; parameter start_index since 2.1.1; changed to consume input adapters, removed start_index parameter, and added strict parameter since 3.0.0; added allow_exceptions parameter since 3.2.0; added tag_handler parameter since 3.9.0.

Note

Any CBOR output created to_cbor can be successfully parsed by from_cbor.

Warning

The mapping is incomplete in the sense that not all CBOR types can be converted to a JSON value. The following CBOR types are not supported and will yield parse errors (parse_error.112):

• date/time (0xC0..0xC1)

• bignum (0xC2..0xC3)

• decimal fraction (0xC4)

• bigfloat (0xC5)

• expected conversions (0xD5..0xD7)

• simple values (0xE0..0xF3, 0xF8)

• undefined (0xF7)

Warning

CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps with keys other than UTF-8 strings are rejected (parse_error.113).

Parameters:

• i – [in] an input in CBOR format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

• tag_handler – [in] how to treat CBOR tags (optional, error by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if unsupported features from CBOR were used in the given input v or if the input is not valid CBOR

• parse_error.113 – if a string was expected as map key, but not found

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename IteratorType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_cbor (IteratorType first, IteratorType last, const bool strict=true, const bool allow_exceptions=true, const cbor_tag_handler_t tag_handler=cbor_tag_handler_t::error)

template<typename T> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_cbor (const T *ptr, std::size_t len, const bool strict=true, const bool allow_exceptions=true, const cbor_tag_handler_t tag_handler=cbor_tag_handler_t::error)

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_cbor (detail::span_input_adapter &&i, const bool strict=true, const bool allow_exceptions=true, const cbor_tag_handler_t tag_handler=cbor_tag_handler_t::error)

template<typename InputType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_msgpack (InputType &&i, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in MessagePack format

Deserializes a given input i to a JSON value using the MessagePack serialization format.

The library maps MessagePack types to JSON value types as follows:

MessagePack type	JSON value type	first byte
positive fixint	number_unsigned	0x00..0x7F
fixmap	object	0x80..0x8F
fixarray	array	0x90..0x9F
fixstr	string	0xA0..0xBF
nil	null	0xC0
false	false	0xC2
true	true	0xC3
float 32	number_float	0xCA
float 64	number_float	0xCB
uint 8	number_unsigned	0xCC
uint 16	number_unsigned	0xCD
uint 32	number_unsigned	0xCE
uint 64	number_unsigned	0xCF
int 8	number_integer	0xD0
int 16	number_integer	0xD1
int 32	number_integer	0xD2
int 64	number_integer	0xD3
str 8	string	0xD9
str 16	string	0xDA
str 32	string	0xDB
array 16	array	0xDC
array 32	array	0xDD
map 16	object	0xDE
map 32	object	0xDF
bin 8	binary	0xC4
bin 16	binary	0xC5
bin 32	binary	0xC6
ext 8	binary	0xC7
ext 16	binary	0xC8
ext 32	binary	0xC9
fixext 1	binary	0xD4
fixext 2	binary	0xD5
fixext 4	binary	0xD6
fixext 8	binary	0xD7
fixext 16	binary	0xD8
negative fixint	number_integer	0xE0-0xFF

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in MessagePack format to a JSON value.,from_msgpack}

See also

http://msgpack.org

See also

to_msgpack(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the related CBOR format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 2.0.9; parameter start_index since 2.1.1; changed to consume input adapters, removed start_index parameter, and added strict parameter since 3.0.0; added allow_exceptions parameter since 3.2.0

Note

Any MessagePack output created to_msgpack can be successfully parsed by from_msgpack.

Parameters:

• i – [in] an input in MessagePack format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if unsupported features from MessagePack were used in the given input i or if the input is not valid MessagePack

• parse_error.113 – if a string was expected as map key, but not found

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename IteratorType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_msgpack (IteratorType first, IteratorType last, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in MessagePack format

Deserializes a given input i to a JSON value using the MessagePack serialization format.

The library maps MessagePack types to JSON value types as follows:

MessagePack type	JSON value type	first byte
positive fixint	number_unsigned	0x00..0x7F
fixmap	object	0x80..0x8F
fixarray	array	0x90..0x9F
fixstr	string	0xA0..0xBF
nil	null	0xC0
false	false	0xC2
true	true	0xC3
float 32	number_float	0xCA
float 64	number_float	0xCB
uint 8	number_unsigned	0xCC
uint 16	number_unsigned	0xCD
uint 32	number_unsigned	0xCE
uint 64	number_unsigned	0xCF
int 8	number_integer	0xD0
int 16	number_integer	0xD1
int 32	number_integer	0xD2
int 64	number_integer	0xD3
str 8	string	0xD9
str 16	string	0xDA
str 32	string	0xDB
array 16	array	0xDC
array 32	array	0xDD
map 16	object	0xDE
map 32	object	0xDF
negative fixint	number_integer	0xE0-0xFF

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in MessagePack format to a JSON value.,from_msgpack}

See also

http://msgpack.org

See also

to_msgpack(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 2.0.9; parameter start_index since 2.1.1; changed to consume input adapters, removed start_index parameter, and added strict parameter since 3.0.0; added allow_exceptions parameter since 3.2.0

Note

Any MessagePack output created to_msgpack can be successfully parsed by from_msgpack.

Warning

The mapping is incomplete in the sense that not all MessagePack types can be converted to a JSON value. The following MessagePack types are not supported and will yield parse errors:

• bin 8 - bin 32 (0xC4..0xC6)

• ext 8 - ext 32 (0xC7..0xC9)

• fixext 1 - fixext 16 (0xD4..0xD8)

Parameters:

• i – [in] an input in MessagePack format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if unsupported features from MessagePack were used in the given input i or if the input is not valid MessagePack

• parse_error.113 – if a string was expected as map key, but not found

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename T> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_msgpack (const T *ptr, std::size_t len, const bool strict=true, const bool allow_exceptions=true)

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_msgpack (detail::span_input_adapter &&i, const bool strict=true, const bool allow_exceptions=true)

template<typename InputType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_ubjson (InputType &&i, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in UBJSON format

Deserializes a given input i to a JSON value using the UBJSON (Universal Binary JSON) serialization format.

The library maps UBJSON types to JSON value types as follows:

UBJSON type	JSON value type	marker
no-op	no value, next value is read	N
null	null	Z
false	false	F
true	true	T
float32	number_float	d
float64	number_float	D
uint8	number_unsigned	U
int8	number_integer	i
int16	number_integer	I
int32	number_integer	l
int64	number_integer	L
high-precision number	number_integer, number_unsigned, or number_float - depends on number string	‘H’
string	string	S
char	string	C
array	array (optimized values are supported)	[
object	object (optimized values are supported)	{

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in UBJSON format to a JSON value.,from_ubjson}

See also

http://ubjson.org

See also

to_ubjson(const basic_json&, const bool, const bool) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 3.1.0; added allow_exceptions parameter since 3.2.0

Note

The mapping is complete in the sense that any UBJSON value can be converted to a JSON value.

Parameters:

• i – [in] an input in UBJSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if a parse error occurs

• parse_error.113 – if a string could not be parsed successfully

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename IteratorType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_ubjson (IteratorType first, IteratorType last, const bool strict=true, const bool allow_exceptions=true)

create a JSON value from an input in UBJSON format

Deserializes a given input i to a JSON value using the UBJSON (Universal Binary JSON) serialization format.

The library maps UBJSON types to JSON value types as follows:

UBJSON type	JSON value type	marker
no-op	no value, next value is read	N
null	null	Z
false	false	F
true	true	T
float32	number_float	d
float64	number_float	D
uint8	number_unsigned	U
int8	number_integer	i
int16	number_integer	I
int32	number_integer	l
int64	number_integer	L
string	string	S
char	string	C
array	array (optimized values are supported)	[
object	object (optimized values are supported)	{

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in UBJSON format to a JSON value.,from_ubjson}

See also

http://ubjson.org

See also

to_ubjson(const basic_json&, const bool, const bool) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_bson(detail::input_adapter&&, const bool, const bool) for the related BSON format

Since

version 3.1.0; added allow_exceptions parameter since 3.2.0

Note

The mapping is complete in the sense that any UBJSON value can be converted to a JSON value.

Parameters:

• i – [in] an input in UBJSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

• parse_error.110 – if the given input ends prematurely or the end of file was not reached when strict was set to true

• parse_error.112 – if a parse error occurs

• parse_error.113 – if a string could not be parsed successfully

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename T> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_ubjson (const T *ptr, std::size_t len, const bool strict=true, const bool allow_exceptions=true)

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_ubjson (detail::span_input_adapter &&i, const bool strict=true, const bool allow_exceptions=true)

template<typename InputType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_bson (InputType &&i, const bool strict=true, const bool allow_exceptions=true)

Create a JSON value from an input in BSON format.

Deserializes a given input i to a JSON value using the BSON (Binary JSON) serialization format.

The library maps BSON record types to JSON value types as follows:

BSON type	BSON marker byte	JSON value type
double	0x01	number_float
string	0x02	string
document	0x03	object
array	0x04	array
binary	0x05	still unsupported
undefined	0x06	still unsupported
ObjectId	0x07	still unsupported
boolean	0x08	boolean
UTC Date-Time	0x09	still unsupported
null	0x0A	null
Regular Expr.	0x0B	still unsupported
DB Pointer	0x0C	still unsupported
JavaScript Code	0x0D	still unsupported
Symbol	0x0E	still unsupported
JavaScript Code	0x0F	still unsupported
int32	0x10	number_integer
Timestamp	0x11	still unsupported
128-bit decimal float	0x13	still unsupported
Max Key	0x7F	still unsupported
Min Key	0xFF	still unsupported

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in BSON format to a JSON value.,from_bson}

See also

http://bsonspec.org/spec.html

See also

to_bson(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool, const cbor_tag_handler_t) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

Warning

The mapping is incomplete. The unsupported mappings are indicated in the table above.

Parameters:

• i – [in] an input in BSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

parse_error.114 – if an unsupported BSON record type is encountered

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename IteratorType> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_bson (IteratorType first, IteratorType last, const bool strict=true, const bool allow_exceptions=true)

Create a JSON value from an input in BSON format.

Deserializes a given input i to a JSON value using the BSON (Binary JSON) serialization format.

The library maps BSON record types to JSON value types as follows:

BSON type	BSON marker byte	JSON value type
double	0x01	number_float
string	0x02	string
document	0x03	object
array	0x04	array
binary	0x05	still unsupported
undefined	0x06	still unsupported
ObjectId	0x07	still unsupported
boolean	0x08	boolean
UTC Date-Time	0x09	still unsupported
null	0x0A	null
Regular Expr.	0x0B	still unsupported
DB Pointer	0x0C	still unsupported
JavaScript Code	0x0D	still unsupported
Symbol	0x0E	still unsupported
JavaScript Code	0x0F	still unsupported
int32	0x10	number_integer
Timestamp	0x11	still unsupported
128-bit decimal float	0x13	still unsupported
Max Key	0x7F	still unsupported
Min Key	0xFF	still unsupported

@complexity Linear in the size of the input i.

@liveexample{The example shows the deserialization of a byte vector in BSON format to a JSON value.,from_bson}

See also

http://bsonspec.org/spec.html

See also

to_bson(const basic_json&) for the analogous serialization

See also

from_cbor(detail::input_adapter&&, const bool, const bool) for the related CBOR format

See also

from_msgpack(detail::input_adapter&&, const bool, const bool) for the related MessagePack format

See also

from_ubjson(detail::input_adapter&&, const bool, const bool) for the related UBJSON format

Warning

The mapping is incomplete. The unsupported mappings are indicated in the table above.

Parameters:

• i – [in] an input in BSON format convertible to an input adapter

• strict – [in] whether to expect the input to be consumed until EOF (true by default)

• allow_exceptions – [in] whether to throw exceptions in case of a parse error (optional, true by default)

Throws:

parse_error.114 – if an unsupported BSON record type is encountered

Returns:

deserialized JSON value; in case of a parse error and allow_exceptions set to false, the return value will be value_t::discarded.

template<typename T> static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_bson (const T *ptr, std::size_t len, const bool strict=true, const bool allow_exceptions=true)

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json from_bson (detail::span_input_adapter &&i, const bool strict=true, const bool allow_exceptions=true)

JSON Patch functions

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json diff (const basic_json &source, const basic_json &target, const std::string &path="")

creates a diff as a JSON patch

Creates a JSON Patch so that value source can be changed into the value target by calling patch function.

@complexity Linear in the lengths of source and target.

Invariant

For two JSON values source and target, the following code yields always true:

source.patch(diff(source, target)) == target;

@liveexample{The following code shows how a JSON patch is created as a diff for two JSON values.,diff}

See also

patch &#8212; apply a JSON patch

See also

merge_patch &#8212; apply a JSON Merge Patch

See also

RFC 6902 (JSON Patch)

Since

version 2.0.0

Note

Currently, only remove, add, and replace operations are generated.

Parameters:

• source – [in] JSON value to compare from

• target – [in] JSON value to compare against

• path – [in] helper value to create JSON pointers

Returns:

a JSON patch to convert the source to target

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json diff (const basic_json &source, const basic_json &target, const std::string &path="")

creates a diff as a JSON patch

Creates a JSON Patch so that value source can be changed into the value target by calling patch function.

@complexity Linear in the lengths of source and target.

Invariant

For two JSON values source and target, the following code yields always true:

source.patch(diff(source, target)) == target;

@liveexample{The following code shows how a JSON patch is created as a diff for two JSON values.,diff}

See also

patch &#8212; apply a JSON patch

See also

merge_patch &#8212; apply a JSON Merge Patch

See also

RFC 6902 (JSON Patch)

Since

version 2.0.0

Note

Currently, only remove, add, and replace operations are generated.

Parameters:

• source – [in] JSON value to compare from

• target – [in] JSON value to compare against

• path – [in] helper value to create JSON pointers

Returns:

a JSON patch to convert the source to target

inline basic_json patch(const basic_json &json_patch) const

applies a JSON patch

JSON Patch defines a JSON document structure for expressing a sequence of operations to apply to a JSON) document. With this function, a JSON Patch is applied to the current JSON value by executing all operations from the patch.

@complexity Linear in the size of the JSON value and the length of the JSON patch. As usually only a fraction of the JSON value is affected by the patch, the complexity can usually be neglected.

@liveexample{The following code shows how a JSON patch is applied to a value.,patch}

See also

diff &#8212; create a JSON patch by comparing two JSON values

See also

RFC 6902 (JSON Patch)

See also

RFC 6901 (JSON Pointer)

Since

version 2.0.0

Note

The application of a patch is atomic: Either all operations succeed and the patched document is returned or an exception is thrown. In any case, the original value is not changed: the patch is applied to a copy of the value.

Parameters:

json_patch – [in] JSON patch document

Throws:

• parse_error.104 – if the JSON patch does not consist of an array of objects

• parse_error.105 – if the JSON patch is malformed (e.g., mandatory attributes are missing); example: "operation add must have member path"

• out_of_range.401 – if an array index is out of range.

• out_of_range.403 – if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example:

  "key baz not

  found"

• out_of_range.405 – if JSON pointer has no parent (“add”, “remove”, “move”)

• other_error.501 – if “test” operation was unsuccessful

Returns:

patched document

inline basic_json patch(const basic_json &json_patch) const

applies a JSON patch

JSON Patch defines a JSON document structure for expressing a sequence of operations to apply to a JSON) document. With this function, a JSON Patch is applied to the current JSON value by executing all operations from the patch.

@complexity Linear in the size of the JSON value and the length of the JSON patch. As usually only a fraction of the JSON value is affected by the patch, the complexity can usually be neglected.

@liveexample{The following code shows how a JSON patch is applied to a value.,patch}

See also

diff &#8212; create a JSON patch by comparing two JSON values

See also

RFC 6902 (JSON Patch)

See also

RFC 6901 (JSON Pointer)

Since

version 2.0.0

Note

The application of a patch is atomic: Either all operations succeed and the patched document is returned or an exception is thrown. In any case, the original value is not changed: the patch is applied to a copy of the value.

Parameters:

json_patch – [in] JSON patch document

Throws:

• parse_error.104 – if the JSON patch does not consist of an array of objects

• parse_error.105 – if the JSON patch is malformed (e.g., mandatory attributes are missing); example: "operation add must have member path"

• out_of_range.401 – if an array index is out of range.

• out_of_range.403 – if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example:

  "key baz not

  found"

• out_of_range.405 – if JSON pointer has no parent (“add”, “remove”, “move”)

• other_error.501 – if “test” operation was unsuccessful

Returns:

patched document

object inspection

Functions to inspect the type of a JSON value.

inline string_t dump(const int indent = -1, const char indent_char = ' ', const bool ensure_ascii = false, const error_handler_t error_handler = error_handler_t::strict) const

serialization

Serialization function for JSON values. The function tries to mimic Python’s json.dumps() function, and currently supports its indent and ensure_ascii parameters.

@complexity Linear.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@liveexample{The following example shows the effect of different indent\, indent_char\, and ensure_ascii parameters to the result of the serialization.,dump}

See also

https://docs.python.org/2/library/json.html#json.dump

Since

version 1.0.0; indentation character indent_char, option ensure_ascii and exceptions added in version 3.0.0; error handlers added in version 3.4.0.

Parameters:

• indent – [in] If indent is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of 0 will only insert newlines. -1 (the default) selects the most compact representation.

• indent_char – [in] The character to use for indentation if indent is greater than 0. The default is (space).

• ensure_ascii – [in] If ensure_ascii is true, all non-ASCII characters in the output are escaped with \uXXXX sequences, and the result consists of ASCII characters only.

• error_handler – [in] how to react on decoding errors; there are three possible values: strict (throws and exception in case a decoding error occurs; default), replace (replace invalid UTF-8 sequences with U+FFFD), and ignore (ignore invalid UTF-8 sequences during serialization).

Throws:

type_error.316 – if a string stored inside the JSON value is not UTF-8 encoded

Returns:

string containing the serialization of the JSON value

inline constexpr value_t type() const noexcept

return the type of the JSON value (explicit)

Return the type of the JSON value as a value from the value_t enumeration.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies type() for all JSON types.,type}

See also

operator value_t() &#8212; return the type of the JSON value (implicit)

See also

type_name() &#8212; return the type as string

Since

version 1.0.0

Returns:

the type of the JSON value

Value type	return value
null	value_t::null
boolean	value_t::boolean
string	value_t::string
number (integer)	value_t::number_integer
number (unsigned integer)	value_t::number_unsigned
number (floating-point)	value_t::number_float
object	value_t::object
array	value_t::array
discarded	value_t::discarded

inline constexpr bool is_primitive() const noexcept

return whether type is primitive

This function returns true if and only if the JSON type is primitive (string, number, boolean, or null).

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_primitive() for all JSON types.,is_primitive}

See also

is_structured() &#8212; returns whether JSON value is structured

See also

is_null() &#8212; returns whether JSON value is null

See also

is_string() &#8212; returns whether JSON value is a string

See also

is_boolean() &#8212; returns whether JSON value is a boolean

See also

is_number() &#8212; returns whether JSON value is a number

Since

version 1.0.0

Returns:

true if type is primitive (string, number, boolean, or null), false otherwise.

inline constexpr bool is_structured() const noexcept

return whether type is structured

This function returns true if and only if the JSON type is structured (array or object).

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_structured() for all JSON types.,is_structured}

See also

is_primitive() &#8212; returns whether value is primitive

See also

is_array() &#8212; returns whether value is an array

See also

is_object() &#8212; returns whether value is an object

Since

version 1.0.0

Returns:

true if type is structured (array or object), false otherwise.

inline constexpr bool is_null() const noexcept

return whether value is null

This function returns true if and only if the JSON value is null.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_null() for all JSON types.,is_null}

Since

version 1.0.0

Returns:

true if type is null, false otherwise.

inline constexpr bool is_boolean() const noexcept

return whether value is a boolean

This function returns true if and only if the JSON value is a boolean.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_boolean() for all JSON types.,is_boolean}

Since

version 1.0.0

Returns:

true if type is boolean, false otherwise.

inline constexpr bool is_number() const noexcept

return whether value is a number

This function returns true if and only if the JSON value is a number. This includes both integer (signed and unsigned) and floating-point values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number() for all JSON types.,is_number}

See also

is_number_integer() &#8212; check if value is an integer or unsigned integer number

See also

is_number_unsigned() &#8212; check if value is an unsigned integer number

See also

is_number_float() &#8212; check if value is a floating-point number

Since

version 1.0.0

Returns:

true if type is number (regardless whether integer, unsigned integer or floating-type), false otherwise.

inline constexpr bool is_number_integer() const noexcept

return whether value is an integer number

This function returns true if and only if the JSON value is a signed or unsigned integer number. This excludes floating-point values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number_integer() for all JSON types.,is_number_integer}

See also

is_number() &#8212; check if value is a number

See also

is_number_unsigned() &#8212; check if value is an unsigned integer number

See also

is_number_float() &#8212; check if value is a floating-point number

Since

version 1.0.0

Returns:

true if type is an integer or unsigned integer number, false otherwise.

inline constexpr bool is_number_unsigned() const noexcept

return whether value is an unsigned integer number

This function returns true if and only if the JSON value is an unsigned integer number. This excludes floating-point and signed integer values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number_unsigned() for all JSON types.,is_number_unsigned}

See also

is_number() &#8212; check if value is a number

See also

is_number_integer() &#8212; check if value is an integer or unsigned integer number

See also

is_number_float() &#8212; check if value is a floating-point number

Since

version 2.0.0

Returns:

true if type is an unsigned integer number, false otherwise.

inline constexpr bool is_number_float() const noexcept

return whether value is a floating-point number

This function returns true if and only if the JSON value is a floating-point number. This excludes signed and unsigned integer values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number_float() for all JSON types.,is_number_float}

See also

is_number() &#8212; check if value is number

See also

is_number_integer() &#8212; check if value is an integer number

See also

is_number_unsigned() &#8212; check if value is an unsigned integer number

Since

version 1.0.0

Returns:

true if type is a floating-point number, false otherwise.

inline constexpr bool is_object() const noexcept

return whether value is an object

This function returns true if and only if the JSON value is an object.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_object() for all JSON types.,is_object}

Since

version 1.0.0

Returns:

true if type is object, false otherwise.

inline constexpr bool is_array() const noexcept

return whether value is an array

This function returns true if and only if the JSON value is an array.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_array() for all JSON types.,is_array}

Since

version 1.0.0

Returns:

true if type is array, false otherwise.

inline constexpr bool is_string() const noexcept

return whether value is a string

This function returns true if and only if the JSON value is a string.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_string() for all JSON types.,is_string}

Since

version 1.0.0

Returns:

true if type is string, false otherwise.

inline constexpr bool is_discarded() const noexcept

return whether value is discarded

This function returns true if and only if the JSON value was discarded during parsing with a callback function (see parser_callback_t).

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_discarded() for all JSON types.,is_discarded}

Since

version 1.0.0

Note

This function will always be false for JSON values after parsing. That is, discarded values can only occur during parsing, but will be removed when inside a structured value or replaced by null in other cases.

Returns:

true if type is discarded, false otherwise.

inline constexpr operator value_t() const noexcept

return the type of the JSON value (implicit)

Implicitly return the type of the JSON value as a value from the value_t enumeration.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies the value_t operator for all JSON types.,operator__value_t}

See also

type() &#8212; return the type of the JSON value (explicit)

See also

type_name() &#8212; return the type as string

Since

version 1.0.0

Returns:

the type of the JSON value

inline string_t dump(const int indent = -1, const char indent_char = ' ', const bool ensure_ascii = false, const error_handler_t error_handler = error_handler_t::strict) const

serialization

Serialization function for JSON values. The function tries to mimic Python’s json.dumps() function, and currently supports its indent and ensure_ascii parameters.

@complexity Linear.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@liveexample{The following example shows the effect of different indent\, indent_char\, and ensure_ascii parameters to the result of the serialization.,dump}

See also

https://docs.python.org/2/library/json.html#json.dump

Since

version 1.0.0; indentation character indent_char, option ensure_ascii and exceptions added in version 3.0.0; error handlers added in version 3.4.0; serialization of binary values added in version 3.8.0.

Note

Binary values are serialized as object containing two keys:

• ”bytes”: an array of bytes as integers

• ”subtype”: the subtype as integer or “null” if the binary has no subtype

Parameters:

• indent – [in] If indent is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of 0 will only insert newlines. -1 (the default) selects the most compact representation.

• indent_char – [in] The character to use for indentation if indent is greater than 0. The default is (space).

• ensure_ascii – [in] If ensure_ascii is true, all non-ASCII characters in the output are escaped with \uXXXX sequences, and the result consists of ASCII characters only.

• error_handler – [in] how to react on decoding errors; there are three possible values: strict (throws and exception in case a decoding error occurs; default), replace (replace invalid UTF-8 sequences with U+FFFD), and ignore (ignore invalid UTF-8 sequences during serialization; all bytes are copied to the output unchanged).

Throws:

type_error.316 – if a string stored inside the JSON value is not UTF-8 encoded and error_handler is set to strict

Returns:

string containing the serialization of the JSON value

inline constexpr value_t type() const noexcept

return the type of the JSON value (explicit)

Return the type of the JSON value as a value from the value_t enumeration.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies type() for all JSON types.,type}

See also

operator value_t() &#8212; return the type of the JSON value (implicit)

See also

type_name() &#8212; return the type as string

Since

version 1.0.0

Returns:

the type of the JSON value

Value type	return value
null	value_t::null
boolean	value_t::boolean
string	value_t::string
number (integer)	value_t::number_integer
number (unsigned integer)	value_t::number_unsigned
number (floating-point)	value_t::number_float
object	value_t::object
array	value_t::array
binary	value_t::binary
discarded	value_t::discarded

inline constexpr bool is_primitive() const noexcept

return whether type is primitive

This function returns true if and only if the JSON type is primitive (string, number, boolean, or null).

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_primitive() for all JSON types.,is_primitive}

See also

is_structured() &#8212; returns whether JSON value is structured

See also

is_null() &#8212; returns whether JSON value is null

See also

is_string() &#8212; returns whether JSON value is a string

See also

is_boolean() &#8212; returns whether JSON value is a boolean

See also

is_number() &#8212; returns whether JSON value is a number

See also

is_binary() &#8212; returns whether JSON value is a binary array

Since

version 1.0.0

Returns:

true if type is primitive (string, number, boolean, or null), false otherwise.

inline constexpr bool is_structured() const noexcept

return whether type is structured

This function returns true if and only if the JSON type is structured (array or object).

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_structured() for all JSON types.,is_structured}

See also

is_primitive() &#8212; returns whether value is primitive

See also

is_array() &#8212; returns whether value is an array

See also

is_object() &#8212; returns whether value is an object

Since

version 1.0.0

Returns:

true if type is structured (array or object), false otherwise.

inline constexpr bool is_null() const noexcept

return whether value is null

This function returns true if and only if the JSON value is null.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_null() for all JSON types.,is_null}

Since

version 1.0.0

Returns:

true if type is null, false otherwise.

inline constexpr bool is_boolean() const noexcept

return whether value is a boolean

This function returns true if and only if the JSON value is a boolean.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_boolean() for all JSON types.,is_boolean}

Since

version 1.0.0

Returns:

true if type is boolean, false otherwise.

inline constexpr bool is_number() const noexcept

return whether value is a number

This function returns true if and only if the JSON value is a number. This includes both integer (signed and unsigned) and floating-point values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number() for all JSON types.,is_number}

See also

is_number_integer() &#8212; check if value is an integer or unsigned integer number

See also

is_number_unsigned() &#8212; check if value is an unsigned integer number

See also

is_number_float() &#8212; check if value is a floating-point number

Since

version 1.0.0

Returns:

true if type is number (regardless whether integer, unsigned integer or floating-type), false otherwise.

inline constexpr bool is_number_integer() const noexcept

return whether value is an integer number

This function returns true if and only if the JSON value is a signed or unsigned integer number. This excludes floating-point values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number_integer() for all JSON types.,is_number_integer}

See also

is_number() &#8212; check if value is a number

See also

is_number_unsigned() &#8212; check if value is an unsigned integer number

See also

is_number_float() &#8212; check if value is a floating-point number

Since

version 1.0.0

Returns:

true if type is an integer or unsigned integer number, false otherwise.

inline constexpr bool is_number_unsigned() const noexcept

return whether value is an unsigned integer number

This function returns true if and only if the JSON value is an unsigned integer number. This excludes floating-point and signed integer values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number_unsigned() for all JSON types.,is_number_unsigned}

See also

is_number() &#8212; check if value is a number

See also

is_number_integer() &#8212; check if value is an integer or unsigned integer number

See also

is_number_float() &#8212; check if value is a floating-point number

Since

version 2.0.0

Returns:

true if type is an unsigned integer number, false otherwise.

inline constexpr bool is_number_float() const noexcept

return whether value is a floating-point number

This function returns true if and only if the JSON value is a floating-point number. This excludes signed and unsigned integer values.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_number_float() for all JSON types.,is_number_float}

See also

is_number() &#8212; check if value is number

See also

is_number_integer() &#8212; check if value is an integer number

See also

is_number_unsigned() &#8212; check if value is an unsigned integer number

Since

version 1.0.0

Returns:

true if type is a floating-point number, false otherwise.

inline constexpr bool is_object() const noexcept

return whether value is an object

This function returns true if and only if the JSON value is an object.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_object() for all JSON types.,is_object}

Since

version 1.0.0

Returns:

true if type is object, false otherwise.

inline constexpr bool is_array() const noexcept

return whether value is an array

This function returns true if and only if the JSON value is an array.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_array() for all JSON types.,is_array}

Since

version 1.0.0

Returns:

true if type is array, false otherwise.

inline constexpr bool is_string() const noexcept

return whether value is a string

This function returns true if and only if the JSON value is a string.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_string() for all JSON types.,is_string}

Since

version 1.0.0

Returns:

true if type is string, false otherwise.

inline constexpr bool is_binary() const noexcept

return whether value is a binary array

This function returns true if and only if the JSON value is a binary array.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_binary() for all JSON types.,is_binary}

Since

version 3.8.0

Returns:

true if type is binary array, false otherwise.

inline constexpr bool is_discarded() const noexcept

return whether value is discarded

This function returns true if and only if the JSON value was discarded during parsing with a callback function (see parser_callback_t).

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies is_discarded() for all JSON types.,is_discarded}

Since

version 1.0.0

Note

This function will always be false for JSON values after parsing. That is, discarded values can only occur during parsing, but will be removed when inside a structured value or replaced by null in other cases.

Returns:

true if type is discarded, false otherwise.

inline constexpr operator value_t() const noexcept

return the type of the JSON value (implicit)

Implicitly return the type of the JSON value as a value from the value_t enumeration.

@complexity Constant.

@exceptionsafety No-throw guarantee: this member function never throws exceptions.

@liveexample{The following code exemplifies the value_t operator for all JSON types.,operator__value_t}

See also

type() &#8212; return the type of the JSON value (explicit)

See also

type_name() &#8212; return the type as string

Since

version 1.0.0

Returns:

the type of the JSON value

value access

Direct access to the stored value of a JSON value.

template<typename BasicJsonType, detail::enable_if_t<std::is_same<typename std::remove_const<BasicJsonType>::type, basic_json_t>::value, int> = 0>
inline basic_json get() const

get special-case overload

This overloads avoids a lot of template boilerplate, it can be seen as the identity method

@complexity Constant.

Since

version 2.1.0

Template Parameters:

BasicJsonType – == basic_json

Returns:

a copy of *this

template<typename BasicJsonType, detail::enable_if_t<not std::is_same<BasicJsonType, basic_json>::value and detail::is_basic_json<BasicJsonType>::value, int> = 0>
inline BasicJsonType get() const

get special-case overload

This overloads converts the current basic_json in a different basic_json type

@complexity Depending on the implementation of the called from_json() method.

Since

version 3.2.0

Template Parameters:

• BasicJsonType – == basic_json

• BasicJsonType –

Returns:

a copy of *this, converted into

template<typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>, detail::enable_if_t<not detail::is_basic_json<ValueType>::value and detail::has_from_json<basic_json_t, ValueType>::value and not detail::has_non_default_from_json<basic_json_t, ValueType>::value, int> = 0>
inline ValueType get() const noexcept(noexcept(JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), std::declval<ValueType&>())))

get a value (explicit)

Explicit type conversion between the JSON value and a compatible value which is CopyConstructible and DefaultConstructible. The value is converted by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

ValueType ret;
JSONSerializer<ValueType>::from_json(*this, ret);
return ret;

This overloads is chosen if:

• ValueType is not basic_json,

• json_serializer<ValueType> has a from_json() method of the form void from_json(const basic_json&, ValueType&), and

• json_serializer<ValueType> does not have a from_json() method of the form ValueType from_json(const basic_json&)

@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,get__ValueType_const}

Since

version 2.1.0

Template Parameters:

• ValueTypeCV – the provided value type

• ValueType – the returned value type

Throws:

what – json_serializer<ValueType> from_json() method throws

Returns:

copy of the JSON value, converted to ValueType

template<typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>, detail::enable_if_t<not std::is_same<basic_json_t, ValueType>::value and detail::has_non_default_from_json<basic_json_t, ValueType>::value, int> = 0>
inline ValueType get() const noexcept(noexcept(JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>())))

get a value (explicit); special case

Explicit type conversion between the JSON value and a compatible value which is not CopyConstructible and not DefaultConstructible. The value is converted by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

return JSONSerializer<ValueTypeCV>::from_json(*this);

This overloads is chosen if:

• ValueType is not basic_json and

• json_serializer<ValueType> has a from_json() method of the form ValueType from_json(const basic_json&)

Since

version 2.1.0

Note

If json_serializer<ValueType> has both overloads of from_json(), this one is chosen.

Template Parameters:

• ValueTypeCV – the provided value type

• ValueType – the returned value type

Throws:

what – json_serializer<ValueType> from_json() method throws

Returns:

copy of the JSON value, converted to ValueType

template<typename ValueType, detail::enable_if_t<not detail::is_basic_json<ValueType>::value and detail::has_from_json<basic_json_t, ValueType>::value, int> = 0>
inline ValueType &get_to(ValueType &v) const noexcept(noexcept(JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))

get a value (explicit)

Explicit type conversion between the JSON value and a compatible value. The value is filled into the input parameter by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

ValueType v;
JSONSerializer<ValueType>::from_json(*this, v);

This overloads is chosen if:

• ValueType is not basic_json,

• json_serializer<ValueType> has a from_json() method of the form void from_json(const basic_json&, ValueType&), and

@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,get_to}

Since

version 3.3.0

Template Parameters:

ValueType – the input parameter type.

Throws:

what – json_serializer<ValueType> from_json() method throws

Returns:

the input parameter, allowing chaining calls.

template<typename T, std::size_t N, typename Array = T (&)[N], detail::enable_if_t<detail::has_from_json<basic_json_t, Array>::value, int> = 0>
inline Array get_to(T (&v)[N]) const noexcept(noexcept(JSONSerializer<Array>::from_json(std::declval<const basic_json_t&>(), v)))

template<typename PointerType, typename std::enable_if<std::is_pointer<PointerType>::value, int>::type = 0>
inline auto get_ptr() noexcept -> decltype(std::declval<basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))

get a pointer value (implicit)

Implicit pointer access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get_ptr}

Since

version 1.0.0

Warning

Writing data to the pointee of the result yields an undefined state.

Template Parameters:

PointerType – pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t. Enforced by a static assertion.

Returns:

pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value; nullptr otherwise

template<typename PointerType, typename std::enable_if<std::is_pointer<PointerType>::value and std::is_const<typename std::remove_pointer<PointerType>::type>::value, int>::type = 0>
inline constexpr auto get_ptr() const noexcept -> decltype(std::declval<const basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))

get a pointer value (implicit)

get a pointer value (implicit)

Implicit pointer access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get_ptr}

Since

version 1.0.0

Warning

Writing data to the pointee of the result yields an undefined state.

Template Parameters:

PointerType – pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t. Enforced by a static assertion.

Returns:

pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value; nullptr otherwise

template<typename PointerType, typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0> inline auto get () noexcept -> decltype(std::declval< basic_json_t & >().template get_ptr< PointerType >())

get a pointer value (explicit)

Explicit pointer access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get__PointerType}

See also

get_ptr() for explicit pointer-member access

Since

version 1.0.0

Warning

The pointer becomes invalid if the underlying JSON object changes.

Template Parameters:

PointerType – pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t.

Returns:

pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value; nullptr otherwise

template<typename PointerType, typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0> inline constexpr auto get () const noexcept -> decltype(std::declval< const basic_json_t & >().template get_ptr< PointerType >())

get a pointer value (explicit)

get special-case overload

This overloads avoids a lot of template boilerplate, it can be seen as the identity method

@complexity Constant.

Since

version 2.1.0

Template Parameters:

BasicJsonType – == basic_json

Returns:

a copy of *this

template<typename ReferenceType, typename std::enable_if<std::is_reference<ReferenceType>::value, int>::type = 0>
inline ReferenceType get_ref()

get a reference value (implicit)

Implicit reference access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example shows several calls to get_ref().,get_ref}

Since

version 1.1.0

Warning

Writing data to the referee of the result yields an undefined state.

Template Parameters:

ReferenceType – reference type; must be a reference to array_t, object_t, string_t, boolean_t, number_integer_t, or number_float_t. Enforced by static assertion.

Throws:

type_error.303 – in case passed type ReferenceType is incompatible with the stored JSON value; see example below

Returns:

reference to the internally stored JSON value if the requested reference type ReferenceType fits to the JSON value; throws type_error.303 otherwise

template<typename ReferenceType, typename std::enable_if<std::is_reference<ReferenceType>::value and std::is_const<typename std::remove_reference<ReferenceType>::type>::value, int>::type = 0>
inline ReferenceType get_ref() const

get a reference value (implicit)

get a reference value (implicit)

Implicit reference access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example shows several calls to get_ref().,get_ref}

Since

version 1.1.0

Warning

Writing data to the referee of the result yields an undefined state.

Template Parameters:

ReferenceType – reference type; must be a reference to array_t, object_t, string_t, boolean_t, number_integer_t, or number_float_t. Enforced by static assertion.

Throws:

type_error.303 – in case passed type ReferenceType is incompatible with the stored JSON value; see example below

Returns:

reference to the internally stored JSON value if the requested reference type ReferenceType fits to the JSON value; throws type_error.303 otherwise

template<typename ValueType, typename std::enable_if<not std::is_pointer<ValueType>::value and not std::is_same<ValueType, detail::json_ref<basic_json>>::value and not std::is_same<ValueType, typename string_t::value_type>::value and not detail::is_basic_json<ValueType>::value and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value and detail::is_detected<detail::get_template_function, const basic_json_t&, ValueType>::value, int>::type = 0>
inline operator ValueType() const

get a value (implicit)

Implicit type conversion between the JSON value and a compatible value. The call is realized by calling get() const.

@complexity Linear in the size of the JSON value.

@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,operator__ValueType}

Since

version 1.0.0

Template Parameters:

ValueType – non-pointer type compatible to the JSON value, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. The character type of string_t as well as an initializer list of this type is excluded to avoid ambiguities as these types implicitly convert to std::string.

Throws:

type_error.302 – in case passed type ValueType is incompatible to the JSON value type (e.g., the JSON value is of type boolean, but a string is requested); see example below

Returns:

copy of the JSON value, converted to type ValueType

template<typename BasicJsonType, detail::enable_if_t<std::is_same<typename std::remove_const<BasicJsonType>::type, basic_json_t>::value, int> = 0>
inline basic_json get() const

get special-case overload

This overloads avoids a lot of template boilerplate, it can be seen as the identity method

@complexity Constant.

Since

version 2.1.0

Template Parameters:

BasicJsonType – == basic_json

Returns:

a copy of *this

template<typename BasicJsonType, detail::enable_if_t<!std::is_same<BasicJsonType, basic_json>::value && detail::is_basic_json<BasicJsonType>::value, int> = 0>
inline BasicJsonType get() const

get special-case overload

This overloads converts the current basic_json in a different basic_json type

@complexity Depending on the implementation of the called from_json() method.

Since

version 3.2.0

Template Parameters:

• BasicJsonType – == basic_json

• BasicJsonType –

Returns:

a copy of *this, converted into

template<typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>, detail::enable_if_t<!detail::is_basic_json<ValueType>::value && detail::has_from_json<basic_json_t, ValueType>::value && !detail::has_non_default_from_json<basic_json_t, ValueType>::value, int> = 0>
inline ValueType get() const noexcept(noexcept(JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), std::declval<ValueType&>())))

get a value (explicit)

Explicit type conversion between the JSON value and a compatible value which is CopyConstructible and DefaultConstructible. The value is converted by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

ValueType ret;
JSONSerializer<ValueType>::from_json(*this, ret);
return ret;

This overloads is chosen if:

• ValueType is not basic_json,

• json_serializer<ValueType> has a from_json() method of the form void from_json(const basic_json&, ValueType&), and

• json_serializer<ValueType> does not have a from_json() method of the form ValueType from_json(const basic_json&)

@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,get__ValueType_const}

Since

version 2.1.0

Template Parameters:

• ValueTypeCV – the provided value type

• ValueType – the returned value type

Throws:

what – json_serializer<ValueType> from_json() method throws

Returns:

copy of the JSON value, converted to ValueType

template<typename ValueTypeCV, typename ValueType = detail::uncvref_t<ValueTypeCV>, detail::enable_if_t<!std::is_same<basic_json_t, ValueType>::value && detail::has_non_default_from_json<basic_json_t, ValueType>::value, int> = 0>
inline ValueType get() const noexcept(noexcept(JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>())))

get a value (explicit); special case

Explicit type conversion between the JSON value and a compatible value which is not CopyConstructible and not DefaultConstructible. The value is converted by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

return JSONSerializer<ValueTypeCV>::from_json(*this);

This overloads is chosen if:

• ValueType is not basic_json and

• json_serializer<ValueType> has a from_json() method of the form ValueType from_json(const basic_json&)

Since

version 2.1.0

Note

If json_serializer<ValueType> has both overloads of from_json(), this one is chosen.

Template Parameters:

• ValueTypeCV – the provided value type

• ValueType – the returned value type

Throws:

what – json_serializer<ValueType> from_json() method throws

Returns:

copy of the JSON value, converted to ValueType

template<typename ValueType, detail::enable_if_t<!detail::is_basic_json<ValueType>::value && detail::has_from_json<basic_json_t, ValueType>::value, int> = 0>
inline ValueType &get_to(ValueType &v) const noexcept(noexcept(JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))

get a value (explicit)

Explicit type conversion between the JSON value and a compatible value. The value is filled into the input parameter by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

ValueType v;
JSONSerializer<ValueType>::from_json(*this, v);

This overloads is chosen if:

• ValueType is not basic_json,

• json_serializer<ValueType> has a from_json() method of the form void from_json(const basic_json&, ValueType&), and

@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,get_to}

Since

version 3.3.0

Template Parameters:

ValueType – the input parameter type.

Throws:

what – json_serializer<ValueType> from_json() method throws

Returns:

the input parameter, allowing chaining calls.

template<typename ValueType, detail::enable_if_t<detail::is_basic_json<ValueType>::value, int> = 0>
inline ValueType &get_to(ValueType &v) const

template<typename T, std::size_t N, typename Array = T (&)[N], detail::enable_if_t<detail::has_from_json<basic_json_t, Array>::value, int> = 0>
inline Array get_to(T (&v)[N]) const noexcept(noexcept(JSONSerializer<Array>::from_json(std::declval<const basic_json_t&>(), v)))

template<typename PointerType, typename std::enable_if<std::is_pointer<PointerType>::value, int>::type = 0>
inline auto get_ptr() noexcept -> decltype(std::declval<basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))

get a pointer value (implicit)

Implicit pointer access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get_ptr}

Since

version 1.0.0

Warning

Writing data to the pointee of the result yields an undefined state.

Template Parameters:

PointerType – pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t. Enforced by a static assertion.

Returns:

pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value; nullptr otherwise

template<typename PointerType, typename std::enable_if<std::is_pointer<PointerType>::value && std::is_const<typename std::remove_pointer<PointerType>::type>::value, int>::type = 0>
inline constexpr auto get_ptr() const noexcept -> decltype(std::declval<const basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))

get a pointer value (implicit)

get a pointer value (implicit)

Implicit pointer access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get_ptr}

Since

version 1.0.0

Warning

Writing data to the pointee of the result yields an undefined state.

Template Parameters:

PointerType – pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t. Enforced by a static assertion.

Returns:

pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value; nullptr otherwise

template<typename PointerType, typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0> inline auto get () noexcept -> decltype(std::declval< basic_json_t & >().template get_ptr< PointerType >())

get a pointer value (explicit)

Explicit pointer access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get__PointerType}

See also

get_ptr() for explicit pointer-member access

Since

version 1.0.0

Warning

The pointer becomes invalid if the underlying JSON object changes.

Template Parameters:

PointerType – pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t.

Returns:

pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value; nullptr otherwise

template<typename PointerType, typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0> inline constexpr auto get () const noexcept -> decltype(std::declval< const basic_json_t & >().template get_ptr< PointerType >())

get a pointer value (explicit)

get special-case overload

This overloads avoids a lot of template boilerplate, it can be seen as the identity method

@complexity Constant.

Since

version 2.1.0

Template Parameters:

BasicJsonType – == basic_json

Returns:

a copy of *this

template<typename ReferenceType, typename std::enable_if<std::is_reference<ReferenceType>::value, int>::type = 0>
inline ReferenceType get_ref()

get a reference value (implicit)

Implicit reference access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example shows several calls to get_ref().,get_ref}

Since

version 1.1.0

Warning

Writing data to the referee of the result yields an undefined state.

Template Parameters:

ReferenceType – reference type; must be a reference to array_t, object_t, string_t, boolean_t, number_integer_t, or number_float_t. Enforced by static assertion.

Throws:

type_error.303 – in case passed type ReferenceType is incompatible with the stored JSON value; see example below

Returns:

reference to the internally stored JSON value if the requested reference type ReferenceType fits to the JSON value; throws type_error.303 otherwise

template<typename ReferenceType, typename std::enable_if<std::is_reference<ReferenceType>::value && std::is_const<typename std::remove_reference<ReferenceType>::type>::value, int>::type = 0>
inline ReferenceType get_ref() const

get a reference value (implicit)

get a reference value (implicit)

Implicit reference access to the internally stored JSON value. No copies are made.

@complexity Constant.

@liveexample{The example shows several calls to get_ref().,get_ref}

Since

version 1.1.0

Warning

Writing data to the referee of the result yields an undefined state.

Template Parameters:

ReferenceType – reference type; must be a reference to array_t, object_t, string_t, boolean_t, number_integer_t, or number_float_t. Enforced by static assertion.

Throws:

type_error.303 – in case passed type ReferenceType is incompatible with the stored JSON value; see example below

Returns:

reference to the internally stored JSON value if the requested reference type ReferenceType fits to the JSON value; throws type_error.303 otherwise

template<typename ValueType, typename std::enable_if<!std::is_pointer<ValueType>::value && !std::is_same<ValueType, detail::json_ref<basic_json>>::value && !std::is_same<ValueType, typename string_t::value_type>::value && !detail::is_basic_json<ValueType>::value && !std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value && detail::is_detected<detail::get_template_function, const basic_json_t&, ValueType>::value, int>::type = 0>
inline JSON_EXPLICIT operator ValueType() const

get a value (implicit)

Implicit type conversion between the JSON value and a compatible value. The call is realized by calling get() const.

@complexity Linear in the size of the JSON value.

@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,operator__ValueType}

Since

version 1.0.0

Template Parameters:

ValueType – non-pointer type compatible to the JSON value, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. The character type of string_t as well as an initializer list of this type is excluded to avoid ambiguities as these types implicitly convert to std::string.

Throws:

type_error.302 – in case passed type ValueType is incompatible to the JSON value type (e.g., the JSON value is of type boolean, but a string is requested); see example below

Returns:

copy of the JSON value, converted to type ValueType

inline binary_t &get_binary()

See also

is_binary() to check if the value is binary

Since

version 3.8.0

Throws:

type_error.302 – if the value is not binary

Returns:

reference to the binary value

inline const binary_t &get_binary() const

See also

is_binary() to check if the value is binary

Since

version 3.8.0

Throws:

type_error.302 – if the value is not binary

Returns:

reference to the binary value

element access

Access to the JSON value.

inline reference at(size_type idx)

access specified array element with bounds checking

Returns a reference to the element at specified location idx, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The example below shows how array elements can be read and written using at(). It also demonstrates the different exceptions that can be thrown.,at__size_type}

Since

version 1.0.0

Parameters:

idx – [in] index of the element to access

Throws:

• type_error.304 – if the JSON value is not an array; in this case, calling at with an index makes no sense. See example below.

• out_of_range.401 – if the index idx is out of range of the array; that is, idx >= size(). See example below.

Returns:

reference to the element at index idx

inline const_reference at(size_type idx) const

access specified array element with bounds checking

Returns a const reference to the element at specified location idx, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The example below shows how array elements can be read using at(). It also demonstrates the different exceptions that can be thrown., at__size_type_const}

Since

version 1.0.0

Parameters:

idx – [in] index of the element to access

Throws:

• type_error.304 – if the JSON value is not an array; in this case, calling at with an index makes no sense. See example below.

• out_of_range.401 – if the index idx is out of range of the array; that is, idx >= size(). See example below.

Returns:

const reference to the element at index idx

inline reference at(const typename object_t::key_type &key)

access specified object element with bounds checking

Returns a reference to the element at with specified key key, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read and written using at(). It also demonstrates the different exceptions that can be thrown.,at__object_t_key_type}

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

See also

value() for access by value with a default value

Since

version 1.0.0

Parameters:

key – [in] key of the element to access

Throws:

• type_error.304 – if the JSON value is not an object; in this case, calling at with a key makes no sense. See example below.

• out_of_range.403 – if the key key is is not stored in the object; that is, find(key) == end(). See example below.

Returns:

reference to the element at key key

inline const_reference at(const typename object_t::key_type &key) const

access specified object element with bounds checking

Returns a const reference to the element at with specified key key, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using at(). It also demonstrates the different exceptions that can be thrown., at__object_t_key_type_const}

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

See also

value() for access by value with a default value

Since

version 1.0.0

Parameters:

key – [in] key of the element to access

Throws:

• type_error.304 – if the JSON value is not an object; in this case, calling at with a key makes no sense. See example below.

• out_of_range.403 – if the key key is is not stored in the object; that is, find(key) == end(). See example below.

Returns:

const reference to the element at key key

inline reference operator[](size_type idx)

access specified array element

Returns a reference to the element at specified location idx.

@complexity Constant if idx is in the range of the array. Otherwise linear in idx - size().

@liveexample{The example below shows how array elements can be read and written using [] operator. Note the addition of null values.,operatorarray__size_type}

Since

version 1.0.0

Note

If idx is beyond the range of the array (i.e., idx >= size()), then the array is silently filled up with null values to make idx a valid reference to the last stored element.

Parameters:

idx – [in] index of the element to access

Throws:

type_error.305 – if the JSON value is not an array or null; in that cases, using the [] operator with an index makes no sense.

Returns:

reference to the element at index idx

inline const_reference operator[](size_type idx) const

access specified array element

Returns a const reference to the element at specified location idx.

@complexity Constant.

@liveexample{The example below shows how array elements can be read using the [] operator.,operatorarray__size_type_const}

Since

version 1.0.0

Parameters:

idx – [in] index of the element to access

Throws:

type_error.305 – if the JSON value is not an array; in that case, using the [] operator with an index makes no sense.

Returns:

const reference to the element at index idx

inline reference operator[](const typename object_t::key_type &key)

access specified object element

Returns a reference to the element at with specified key key.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.0.0

Note

If key is not found in the object, then it is silently added to the object and filled with a null value to make key a valid reference. In case the value was null before, it is converted to an object.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object or null; in that cases, using the [] operator with a key makes no sense.

Returns:

reference to the element at key key

inline const_reference operator[](const typename object_t::key_type &key) const

read-only access specified object element

Returns a const reference to the element at with specified key key. No bounds checking is performed.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using the [] operator.,operatorarray__key_type_const}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.0.0

Warning

If the element with key key does not exist, the behavior is undefined.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object; in that case, using the [] operator with a key makes no sense.

Returns:

const reference to the element at key key

Pre:

The element with key key must exist. This precondition is enforced with an assertion.

template<typename T>
inline reference operator[](T *key)

access specified object element

Returns a reference to the element at with specified key key.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.1.0

Note

If key is not found in the object, then it is silently added to the object and filled with a null value to make key a valid reference. In case the value was null before, it is converted to an object.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object or null; in that cases, using the [] operator with a key makes no sense.

Returns:

reference to the element at key key

template<typename T>
inline const_reference operator[](T *key) const

read-only access specified object element

Returns a const reference to the element at with specified key key. No bounds checking is performed.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using the [] operator.,operatorarray__key_type_const}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.1.0

Warning

If the element with key key does not exist, the behavior is undefined.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object; in that case, using the [] operator with a key makes no sense.

Returns:

const reference to the element at key key

Pre:

The element with key key must exist. This precondition is enforced with an assertion.

template<class ValueType, typename std::enable_if<std::is_convertible<basic_json_t, ValueType>::value, int>::type = 0>
inline ValueType value(const typename object_t::key_type &key, const ValueType &default_value) const

access specified object element with default value

Returns either a copy of an object’s element at the specified key key or a given default value if no element with key key exists.

The function is basically equivalent to executing

try {
    return at(key);
} catch(out_of_range) {
    return default_value;
}

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

Since

version 1.0.0

Note

Unlike at(const typename object_t::key_type&), this function does not throw if the given key key was not found.

Note

Unlike operator[](const typename object_t::key_type& key), this function does not implicitly add an element to the position defined by key. This function is furthermore also applicable to const objects.

Parameters:

• key – [in] key of the element to access

• default_value – [in] the value to return if key is not found

Template Parameters:

ValueType – type compatible to JSON values, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.

Throws:

• type_error.302 – if default_value does not match the type of the value at key

• type_error.306 – if the JSON value is not an object; in that case, using value() with a key makes no sense.

Returns:

copy of the element at key key or default_value if key is not found

inline string_t value(const typename object_t::key_type &key, const char *default_value) const

overload for a default value of type const char*

access specified object element with default value

Returns either a copy of an object’s element at the specified key key or a given default value if no element with key key exists.

The function is basically equivalent to executing

try {
    return at(key);
} catch(out_of_range) {
    return default_value;
}

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

Since

version 1.0.0

Note

Unlike at(const typename object_t::key_type&), this function does not throw if the given key key was not found.

Note

Unlike operator[](const typename object_t::key_type& key), this function does not implicitly add an element to the position defined by key. This function is furthermore also applicable to const objects.

Parameters:

• key – [in] key of the element to access

• default_value – [in] the value to return if key is not found

Template Parameters:

ValueType – type compatible to JSON values, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.

Throws:

• type_error.302 – if default_value does not match the type of the value at key

• type_error.306 – if the JSON value is not an object; in that case, using value() with a key makes no sense.

Returns:

copy of the element at key key or default_value if key is not found

template<class ValueType, typename std::enable_if<std::is_convertible<basic_json_t, ValueType>::value, int>::type = 0>
inline ValueType value(const json_pointer &ptr, const ValueType &default_value) const

access specified object element via JSON Pointer with default value

Returns either a copy of an object’s element at the specified key key or a given default value if no element with key key exists.

The function is basically equivalent to executing

try {
    return at(ptr);
} catch(out_of_range) {
    return default_value;
}

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value_ptr}

See also

operator[](const json_pointer&) for unchecked access by reference

Since

version 2.0.2

Note

Unlike at(const json_pointer&), this function does not throw if the given key key was not found.

Parameters:

• ptr – [in] a JSON pointer to the element to access

• default_value – [in] the value to return if ptr found no value

Template Parameters:

ValueType – type compatible to JSON values, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.

Throws:

• type_error.302 – if default_value does not match the type of the value at ptr

• type_error.306 – if the JSON value is not an object; in that case, using value() with a key makes no sense.

Returns:

copy of the element at key key or default_value if key is not found

inline string_t value(const json_pointer &ptr, const char *default_value) const

overload for a default value of type const char*

inline reference front()

access the first element

Returns a reference to the first element in the container. For a JSON container c, the expression c.front() is equivalent to *c.begin().

@complexity Constant.

@liveexample{The following code shows an example for front().,front}

See also

back() &#8212; access the last element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, or boolean values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on null value

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

inline const_reference front() const

access the first element

Returns a reference to the first element in the container. For a JSON container c, the expression c.front() is equivalent to *c.begin().

@complexity Constant.

@liveexample{The following code shows an example for front().,front}

See also

back() &#8212; access the last element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, or boolean values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on null value

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

inline reference back()

access the last element

Returns a reference to the last element in the container. For a JSON container c, the expression c.back() is equivalent to

auto tmp = c.end();
--tmp;
return *tmp;

@complexity Constant.

@liveexample{The following code shows an example for back().,back}

See also

front() &#8212; access the first element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the last element is returned. In case of number, string, or boolean values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on a null value. See example below.

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

inline const_reference back() const

access the last element

Returns a reference to the last element in the container. For a JSON container c, the expression c.back() is equivalent to

auto tmp = c.end();
--tmp;
return *tmp;

@complexity Constant.

@liveexample{The following code shows an example for back().,back}

See also

front() &#8212; access the first element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the last element is returned. In case of number, string, or boolean values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on a null value. See example below.

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

template<class IteratorType, typename std::enable_if<std::is_same<IteratorType, typename basic_json_t::iterator>::value or std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int>::type = 0>
inline IteratorType erase(IteratorType pos)

remove element given an iterator

Removes the element specified by iterator pos. The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos.

If called on a primitive type other than null, the resulting JSON value will be null.

@complexity The complexity depends on the type:

• objects: amortized constant

• arrays: linear in distance between pos and the end of the container

• strings: linear in the length of the string

• other types: constant

@liveexample{The example shows the result of erase() for different JSON types.,erase__IteratorType}

See also

erase(IteratorType, IteratorType) &#8212; removes the elements in the given range

See also

erase(const typename object_t::key_type&) &#8212; removes the element from an object at the given key

See also

erase(const size_type) &#8212; removes the element from an array at the given index

Since

version 1.0.0

Parameters:

pos – [in] iterator to the element to remove

Template Parameters:

IteratorType – an iterator or const_iterator

Throws:

• type_error.307 – if called on a null value; example:

  "cannot use

  erase() with null"

• invalid_iterator.202 – if called on an iterator which does not belong to the current JSON value; example:

  "iterator does not fit current

  value"

• invalid_iterator.205 – if called on a primitive type with invalid iterator (i.e., any iterator which is not begin()); example:

  "iterator

  out of range"

Returns:

Iterator following the last removed element. If the iterator pos refers to the last element, the end() iterator is returned.

Post:

Invalidates iterators and references at or after the point of the erase, including the end() iterator.

template<class IteratorType, typename std::enable_if<std::is_same<IteratorType, typename basic_json_t::iterator>::value or std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int>::type = 0>
inline IteratorType erase(IteratorType first, IteratorType last)

remove elements given an iterator range

Removes the element specified by the range [first; last). The iterator first does not need to be dereferenceable if first == last: erasing an empty range is a no-op.

If called on a primitive type other than null, the resulting JSON value will be null.

@complexity The complexity depends on the type:

• objects: log(size()) + std::distance(first, last)

• arrays: linear in the distance between first and last, plus linear in the distance between last and end of the container

• strings: linear in the length of the string

• other types: constant

@liveexample{The example shows the result of erase() for different JSON types.,erase__IteratorType_IteratorType}

See also

erase(IteratorType) &#8212; removes the element at a given position

See also

erase(const typename object_t::key_type&) &#8212; removes the element from an object at the given key

See also

erase(const size_type) &#8212; removes the element from an array at the given index

Since

version 1.0.0

Parameters:

• first – [in] iterator to the beginning of the range to remove

• last – [in] iterator past the end of the range to remove

Template Parameters:

IteratorType – an iterator or const_iterator

Throws:

• type_error.307 – if called on a null value; example:

  "cannot use

  erase() with null"

• invalid_iterator.203 – if called on iterators which does not belong to the current JSON value; example: "iterators do not fit current value"

• invalid_iterator.204 – if called on a primitive type with invalid iterators (i.e., if first != begin() and last != end()); example: "iterators out of range"

Returns:

Iterator following the last removed element. If the iterator second refers to the last element, the end() iterator is returned.

Post:

Invalidates iterators and references at or after the point of the erase, including the end() iterator.

inline size_type erase(const typename object_t::key_type &key)

remove element from a JSON object given a key

Removes elements from a JSON object with the key value key.

@complexity log(size()) + count(key)

@liveexample{The example shows the effect of erase().,erase__key_type}

See also

erase(IteratorType) &#8212; removes the element at a given position

See also

erase(IteratorType, IteratorType) &#8212; removes the elements in the given range

See also

erase(const size_type) &#8212; removes the element from an array at the given index

Since

version 1.0.0

Parameters:

key – [in] value of the elements to remove

Throws:

type_error.307 – when called on a type other than JSON object; example: "cannot use erase() with null"

Returns:

Number of elements removed. If ObjectType is the default std::map type, the return value will always be 0 (key was not found) or 1 (key was found).

Post:

References and iterators to the erased elements are invalidated. Other references and iterators are not affected.

inline void erase(const size_type idx)

remove element from a JSON array given an index

Removes element from a JSON array at the index idx.

@complexity Linear in distance between idx and the end of the container.

@liveexample{The example shows the effect of erase().,erase__size_type}

See also

erase(IteratorType) &#8212; removes the element at a given position

See also

erase(IteratorType, IteratorType) &#8212; removes the elements in the given range

See also

erase(const typename object_t::key_type&) &#8212; removes the element from an object at the given key

Since

version 1.0.0

Parameters:

idx – [in] index of the element to remove

Throws:

• type_error.307 – when called on a type other than JSON object; example: "cannot use erase() with null"

• out_of_range.401 – when idx >= size(); example:

  "array index 17

  is out of range"

inline reference at(size_type idx)

access specified array element with bounds checking

Returns a reference to the element at specified location idx, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The example below shows how array elements can be read and written using at(). It also demonstrates the different exceptions that can be thrown.,at__size_type}

Since

version 1.0.0

Parameters:

idx – [in] index of the element to access

Throws:

• type_error.304 – if the JSON value is not an array; in this case, calling at with an index makes no sense. See example below.

• out_of_range.401 – if the index idx is out of range of the array; that is, idx >= size(). See example below.

Returns:

reference to the element at index idx

inline const_reference at(size_type idx) const

access specified array element with bounds checking

Returns a const reference to the element at specified location idx, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The example below shows how array elements can be read using at(). It also demonstrates the different exceptions that can be thrown., at__size_type_const}

Since

version 1.0.0

Parameters:

idx – [in] index of the element to access

Throws:

• type_error.304 – if the JSON value is not an array; in this case, calling at with an index makes no sense. See example below.

• out_of_range.401 – if the index idx is out of range of the array; that is, idx >= size(). See example below.

Returns:

const reference to the element at index idx

inline reference at(const typename object_t::key_type &key)

access specified object element with bounds checking

Returns a reference to the element at with specified key key, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read and written using at(). It also demonstrates the different exceptions that can be thrown.,at__object_t_key_type}

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

See also

value() for access by value with a default value

Since

version 1.0.0

Parameters:

key – [in] key of the element to access

Throws:

• type_error.304 – if the JSON value is not an object; in this case, calling at with a key makes no sense. See example below.

• out_of_range.403 – if the key key is is not stored in the object; that is, find(key) == end(). See example below.

Returns:

reference to the element at key key

inline const_reference at(const typename object_t::key_type &key) const

access specified object element with bounds checking

Returns a const reference to the element at with specified key key, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using at(). It also demonstrates the different exceptions that can be thrown., at__object_t_key_type_const}

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

See also

value() for access by value with a default value

Since

version 1.0.0

Parameters:

key – [in] key of the element to access

Throws:

• type_error.304 – if the JSON value is not an object; in this case, calling at with a key makes no sense. See example below.

• out_of_range.403 – if the key key is is not stored in the object; that is, find(key) == end(). See example below.

Returns:

const reference to the element at key key

inline reference operator[](size_type idx)

access specified array element

Returns a reference to the element at specified location idx.

@complexity Constant if idx is in the range of the array. Otherwise linear in idx - size().

@liveexample{The example below shows how array elements can be read and written using [] operator. Note the addition of null values.,operatorarray__size_type}

Since

version 1.0.0

Note

If idx is beyond the range of the array (i.e., idx >= size()), then the array is silently filled up with null values to make idx a valid reference to the last stored element.

Parameters:

idx – [in] index of the element to access

Throws:

type_error.305 – if the JSON value is not an array or null; in that cases, using the [] operator with an index makes no sense.

Returns:

reference to the element at index idx

inline const_reference operator[](size_type idx) const

access specified array element

Returns a const reference to the element at specified location idx.

@complexity Constant.

@liveexample{The example below shows how array elements can be read using the [] operator.,operatorarray__size_type_const}

Since

version 1.0.0

Parameters:

idx – [in] index of the element to access

Throws:

type_error.305 – if the JSON value is not an array; in that case, using the [] operator with an index makes no sense.

Returns:

const reference to the element at index idx

inline reference operator[](const typename object_t::key_type &key)

access specified object element

Returns a reference to the element at with specified key key.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.0.0

Note

If key is not found in the object, then it is silently added to the object and filled with a null value to make key a valid reference. In case the value was null before, it is converted to an object.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object or null; in that cases, using the [] operator with a key makes no sense.

Returns:

reference to the element at key key

inline const_reference operator[](const typename object_t::key_type &key) const

read-only access specified object element

Returns a const reference to the element at with specified key key. No bounds checking is performed.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using the [] operator.,operatorarray__key_type_const}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.0.0

Warning

If the element with key key does not exist, the behavior is undefined.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object; in that case, using the [] operator with a key makes no sense.

Returns:

const reference to the element at key key

Pre:

The element with key key must exist. This precondition is enforced with an assertion.

template<typename T>
inline reference operator[](T *key)

access specified object element

Returns a reference to the element at with specified key key.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.1.0

Note

If key is not found in the object, then it is silently added to the object and filled with a null value to make key a valid reference. In case the value was null before, it is converted to an object.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object or null; in that cases, using the [] operator with a key makes no sense.

Returns:

reference to the element at key key

template<typename T>
inline const_reference operator[](T *key) const

read-only access specified object element

Returns a const reference to the element at with specified key key. No bounds checking is performed.

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be read using the [] operator.,operatorarray__key_type_const}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

value() for access by value with a default value

Since

version 1.1.0

Warning

If the element with key key does not exist, the behavior is undefined.

Parameters:

key – [in] key of the element to access

Throws:

type_error.305 – if the JSON value is not an object; in that case, using the [] operator with a key makes no sense.

Returns:

const reference to the element at key key

Pre:

The element with key key must exist. This precondition is enforced with an assertion.

template<class ValueType, typename std::enable_if<detail::is_getable<basic_json_t, ValueType>::value && !std::is_same<value_t, ValueType>::value, int>::type = 0>
inline ValueType value(const typename object_t::key_type &key, const ValueType &default_value) const

access specified object element with default value

Returns either a copy of an object’s element at the specified key key or a given default value if no element with key key exists.

The function is basically equivalent to executing

try {
    return at(key);
} catch(out_of_range) {
    return default_value;
}

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

Since

version 1.0.0

Note

Unlike at(const typename object_t::key_type&), this function does not throw if the given key key was not found.

Note

Unlike operator[](const typename object_t::key_type& key), this function does not implicitly add an element to the position defined by key. This function is furthermore also applicable to const objects.

Parameters:

• key – [in] key of the element to access

• default_value – [in] the value to return if key is not found

Template Parameters:

ValueType – type compatible to JSON values, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.

Throws:

• type_error.302 – if default_value does not match the type of the value at key

• type_error.306 – if the JSON value is not an object; in that case, using value() with a key makes no sense.

Returns:

copy of the element at key key or default_value if key is not found

inline string_t value(const typename object_t::key_type &key, const char *default_value) const

overload for a default value of type const char*

access specified object element with default value

Returns either a copy of an object’s element at the specified key key or a given default value if no element with key key exists.

The function is basically equivalent to executing

try {
    return at(key);
} catch(out_of_range) {
    return default_value;
}

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value}

See also

at(const typename object_t::key_type&) for access by reference with range checking

See also

operator[](const typename object_t::key_type&) for unchecked access by reference

Since

version 1.0.0

Note

Unlike at(const typename object_t::key_type&), this function does not throw if the given key key was not found.

Note

Unlike operator[](const typename object_t::key_type& key), this function does not implicitly add an element to the position defined by key. This function is furthermore also applicable to const objects.

Parameters:

• key – [in] key of the element to access

• default_value – [in] the value to return if key is not found

Template Parameters:

ValueType – type compatible to JSON values, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.

Throws:

• type_error.302 – if default_value does not match the type of the value at key

• type_error.306 – if the JSON value is not an object; in that case, using value() with a key makes no sense.

Returns:

copy of the element at key key or default_value if key is not found

template<class ValueType, typename std::enable_if<detail::is_getable<basic_json_t, ValueType>::value, int>::type = 0>
inline ValueType value(const json_pointer &ptr, const ValueType &default_value) const

access specified object element via JSON Pointer with default value

Returns either a copy of an object’s element at the specified key key or a given default value if no element with key key exists.

The function is basically equivalent to executing

try {
    return at(ptr);
} catch(out_of_range) {
    return default_value;
}

@complexity Logarithmic in the size of the container.

@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value_ptr}

See also

operator[](const json_pointer&) for unchecked access by reference

Since

version 2.0.2

Note

Unlike at(const json_pointer&), this function does not throw if the given key key was not found.

Parameters:

• ptr – [in] a JSON pointer to the element to access

• default_value – [in] the value to return if ptr found no value

Template Parameters:

ValueType – type compatible to JSON values, for instance int for JSON integer numbers, bool for JSON booleans, or std::vector types for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.

Throws:

• type_error.302 – if default_value does not match the type of the value at ptr

• type_error.306 – if the JSON value is not an object; in that case, using value() with a key makes no sense.

Returns:

copy of the element at key key or default_value if key is not found

inline string_t value(const json_pointer &ptr, const char *default_value) const

overload for a default value of type const char*

inline reference front()

access the first element

Returns a reference to the first element in the container. For a JSON container c, the expression c.front() is equivalent to *c.begin().

@complexity Constant.

@liveexample{The following code shows an example for front().,front}

See also

back() &#8212; access the last element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, boolean, or binary values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on null value

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

inline const_reference front() const

access the first element

Returns a reference to the first element in the container. For a JSON container c, the expression c.front() is equivalent to *c.begin().

@complexity Constant.

@liveexample{The following code shows an example for front().,front}

See also

back() &#8212; access the last element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, or boolean values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on null value

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

inline reference back()

access the last element

Returns a reference to the last element in the container. For a JSON container c, the expression c.back() is equivalent to

auto tmp = c.end();
--tmp;
return *tmp;

@complexity Constant.

@liveexample{The following code shows an example for back().,back}

See also

front() &#8212; access the first element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the last element is returned. In case of number, string, boolean, or binary values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on a null value. See example below.

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

inline const_reference back() const

access the last element

Returns a reference to the last element in the container. For a JSON container c, the expression c.back() is equivalent to

auto tmp = c.end();
--tmp;
return *tmp;

@complexity Constant.

@liveexample{The following code shows an example for back().,back}

See also

front() &#8212; access the first element

Since

version 1.0.0

Returns:

In case of a structured type (array or object), a reference to the last element is returned. In case of number, string, or boolean values, a reference to the value is returned.

Throws:

invalid_iterator.214 – when called on a null value. See example below.

Pre:

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Post:

The JSON value remains unchanged.

template<class IteratorType, typename std::enable_if<std::is_same<IteratorType, typename basic_json_t::iterator>::value || std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int>::type = 0>
inline IteratorType erase(IteratorType pos)

remove element given an iterator

Removes the element specified by iterator pos. The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos.

If called on a primitive type other than null, the resulting JSON value will be null.

@complexity The complexity depends on the type:

• objects: amortized constant

• arrays: linear in distance between pos and the end of the container

• strings and binary: linear in the length of the member

• other types: constant

@liveexample{The example shows the result of erase() for different JSON types.,erase__IteratorType}

See also

erase(IteratorType, IteratorType) &#8212; removes the elements in the given range

See also

erase(const typename object_t::key_type&) &#8212; removes the element from an object at the given key

See also

erase(const size_type) &#8212; removes the element from an array at the given index

Since

version 1.0.0

Parameters:

pos – [in] iterator to the element to remove

Template Parameters:

IteratorType – an iterator or const_iterator

Throws:

• type_error.307 – if called on a null value; example:

  "cannot use

  erase() with null"

• invalid_iterator.202 – if called on an iterator which does not belong to the current JSON value; example:

  "iterator does not fit current

  value"

• invalid_iterator.205 – if called on a primitive type with invalid iterator (i.e., any iterator which is not begin()); example:

  "iterator

  out of range"

Returns:

Iterator following the last removed element. If the iterator pos refers to the last element, the end() iterator is returned.

Post:

Invalidates iterators and references at or after the point of the erase, including the end() iterator.

template<class IteratorType, typename std::enable_if<std::is_same<IteratorType, typename basic_json_t::iterator>::value || std::is_same<IteratorType, typename basic_json_t::const_iterator>::value, int>::type = 0>
inline IteratorType erase(IteratorType first, IteratorType last)

remove elements given an iterator range

Removes the element specified by the range [first; last). The iterator first does not need to be dereferenceable if first == last: erasing an empty range is a no-op.

If called on a primitive type other than null, the resulting JSON value will be null.

@complexity The complexity depends on the type:

• objects: log(size()) + std::distance(first, last)

• arrays: linear in the distance between first and last, plus linear in the distance between last and end of the container

• strings and binary: linear in the length of the member

• other types: constant

@liveexample{The example shows the result of erase() for different JSON types.,erase__IteratorType_IteratorType}

See also

erase(IteratorType) &#8212; removes the element at a given position

See also

erase(const typename object_t::key_type&) &#8212; removes the element from an object at the given key

See also

erase(const size_type) &#8212; removes the element from an array at the given index

Since

version 1.0.0

Parameters:

• first – [in] iterator to the beginning of the range to remove

• last – [in] iterator past the end of the range to remove

Template Parameters:

IteratorType – an iterator or const_iterator

Throws:

• type_error.307 – if called on a null value; example:

  "cannot use

  erase() with null"

• invalid_iterator.203 – if called on iterators which does not belong to the current JSON value; example: "iterators do not fit current value"

• invalid_iterator.204 – if called on a primitive type with invalid iterators (i.e., if first != begin() and last != end()); example: "iterators out of range"

Returns:

Iterator following the last removed element. If the iterator second refers to the last element, the end() iterator is returned.

Post:

Invalidates iterators and references at or after the point of the erase, including the end() iterator.

inline size_type erase(const typename object_t::key_type &key)

remove element from a JSON object given a key

Removes elements from a JSON object with the key value key.

@complexity log(size()) + count(key)

@liveexample{The example shows the effect of erase().,erase__key_type}

See also

erase(IteratorType) &#8212; removes the element at a given position

See also

erase(IteratorType, IteratorType) &#8212; removes the elements in the given range

See also

erase(const size_type) &#8212; removes the element from an array at the given index

Since

version 1.0.0

Parameters:

key – [in] value of the elements to remove

Throws:

type_error.307 – when called on a type other than JSON object; example: "cannot use erase() with null"

Returns:

Number of elements removed. If ObjectType is the default std::map type, the return value will always be 0 (key was not found) or 1 (key was found).

Post:

References and iterators to the erased elements are invalidated. Other references and iterators are not affected.

inline void erase(const size_type idx)

remove element from a JSON array given an index

Removes element from a JSON array at the index idx.

@complexity Linear in distance between idx and the end of the container.

@liveexample{The example shows the effect of erase().,erase__size_type}

See also

erase(IteratorType) &#8212; removes the element at a given position

See also

erase(IteratorType, IteratorType) &#8212; removes the elements in the given range

See also

erase(const typename object_t::key_type&) &#8212; removes the element from an object at the given key

Since

version 1.0.0

Parameters:

idx – [in] index of the element to remove

Throws:

• type_error.307 – when called on a type other than JSON object; example: "cannot use erase() with null"

• out_of_range.401 – when idx >= size(); example:

  "array index 17

  is out of range"

lookup

template<typename KeyT>
inline iterator find(KeyT &&key)

find an element in a JSON object

Finds an element in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, end() is returned.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The example shows how find() is used.,find__key_type}

See also

contains(KeyT&&) const &#8212; checks whether a key exists

Since

version 1.0.0

Note

This method always returns end() when executed on a JSON type that is not an object.

Parameters:

key – [in] key value of the element to search for.

Returns:

Iterator to an element with key equivalent to key. If no such element is found or the JSON value is not an object, past-the-end (see end()) iterator is returned.

template<typename KeyT>
inline const_iterator find(KeyT &&key) const

find an element in a JSON object

find an element in a JSON object

Finds an element in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, end() is returned.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The example shows how find() is used.,find__key_type}

See also

contains(KeyT&&) const &#8212; checks whether a key exists

Since

version 1.0.0

Note

This method always returns end() when executed on a JSON type that is not an object.

Parameters:

key – [in] key value of the element to search for.

Returns:

Iterator to an element with key equivalent to key. If no such element is found or the JSON value is not an object, past-the-end (see end()) iterator is returned.

template<typename KeyT>
inline size_type count(KeyT &&key) const

returns the number of occurrences of a key in a JSON object

Returns the number of elements with key key. If ObjectType is the default std::map type, the return value will always be 0 (key was not found) or 1 (key was found).

@complexity Logarithmic in the size of the JSON object.

@liveexample{The example shows how count() is used.,count}

Since

version 1.0.0

Note

This method always returns 0 when executed on a JSON type that is not an object.

Parameters:

key – [in] key value of the element to count

Returns:

Number of elements with key key. If the JSON value is not an object, the return value will be 0.

template<typename KeyT, typename std::enable_if<not std::is_same<typename std::decay<KeyT>::type, json_pointer>::value, int>::type = 0>
inline bool contains(KeyT &&key) const

check the existence of an element in a JSON object

Check whether an element exists in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, false is returned.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The following code shows an example for contains().,contains}

See also

find(KeyT&&) &#8212; returns an iterator to an object element

See also

contains(const json_pointer&) const &#8212; checks the existence for a JSON pointer

Since

version 3.6.0

Note

This method always returns false when executed on a JSON type that is not an object.

Parameters:

key – [in] key value to check its existence.

Returns:

true if an element with specified key exists. If no such element with such key is found or the JSON value is not an object, false is returned.

inline bool contains(const json_pointer &ptr) const

check the existence of an element in a JSON object given a JSON pointer

Check whether the given JSON pointer ptr can be resolved in the current JSON value.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The following code shows an example for contains().,contains_json_pointer}

See also

contains(KeyT &&) const &#8212; checks the existence of a key

Since

version 3.7.0

Note

This method can be executed on any JSON value type.

Parameters:

ptr – [in] JSON pointer to check its existence.

Throws:

• parse_error.106 – if an array index begins with ‘0’

• parse_error.109 – if an array index was not a number

Returns:

true if the JSON pointer can be resolved to a stored value, false otherwise.

Post:

If j.contains(ptr) returns true, it is safe to call j[ptr].

template<typename KeyT>
inline iterator find(KeyT &&key)

find an element in a JSON object

Finds an element in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, end() is returned.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The example shows how find() is used.,find__key_type}

See also

contains(KeyT&&) const &#8212; checks whether a key exists

Since

version 1.0.0

Note

This method always returns end() when executed on a JSON type that is not an object.

Parameters:

key – [in] key value of the element to search for.

Returns:

Iterator to an element with key equivalent to key. If no such element is found or the JSON value is not an object, past-the-end (see end()) iterator is returned.

template<typename KeyT>
inline const_iterator find(KeyT &&key) const

find an element in a JSON object

find an element in a JSON object

Finds an element in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, end() is returned.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The example shows how find() is used.,find__key_type}

See also

contains(KeyT&&) const &#8212; checks whether a key exists

Since

version 1.0.0

Note

This method always returns end() when executed on a JSON type that is not an object.

Parameters:

key – [in] key value of the element to search for.

Returns:

Iterator to an element with key equivalent to key. If no such element is found or the JSON value is not an object, past-the-end (see end()) iterator is returned.

template<typename KeyT>
inline size_type count(KeyT &&key) const

returns the number of occurrences of a key in a JSON object

Returns the number of elements with key key. If ObjectType is the default std::map type, the return value will always be 0 (key was not found) or 1 (key was found).

@complexity Logarithmic in the size of the JSON object.

@liveexample{The example shows how count() is used.,count}

Since

version 1.0.0

Note

This method always returns 0 when executed on a JSON type that is not an object.

Parameters:

key – [in] key value of the element to count

Returns:

Number of elements with key key. If the JSON value is not an object, the return value will be 0.

template<typename KeyT, typename std::enable_if<!std::is_same<typename std::decay<KeyT>::type, json_pointer>::value, int>::type = 0>
inline bool contains(KeyT &&key) const

check the existence of an element in a JSON object

Check whether an element exists in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, false is returned.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The following code shows an example for contains().,contains}

See also

find(KeyT&&) &#8212; returns an iterator to an object element

See also

contains(const json_pointer&) const &#8212; checks the existence for a JSON pointer

Since

version 3.6.0

Note

This method always returns false when executed on a JSON type that is not an object.

Parameters:

key – [in] key value to check its existence.

Returns:

true if an element with specified key exists. If no such element with such key is found or the JSON value is not an object, false is returned.

inline bool contains(const json_pointer &ptr) const

check the existence of an element in a JSON object given a JSON pointer

Check whether the given JSON pointer ptr can be resolved in the current JSON value.

@complexity Logarithmic in the size of the JSON object.

@liveexample{The following code shows an example for contains().,contains_json_pointer}

See also

contains(KeyT &&) const &#8212; checks the existence of a key

Since

version 3.7.0

Note

This method can be executed on any JSON value type.

Parameters:

ptr – [in] JSON pointer to check its existence.

Throws:

• parse_error.106 – if an array index begins with ‘0’

• parse_error.109 – if an array index was not a number

Returns:

true if the JSON pointer can be resolved to a stored value, false otherwise.

Post:

If j.contains(ptr) returns true, it is safe to call j[ptr].

capacity

inline bool empty() const noexcept

checks whether the container is empty.

Checks if a JSON value has no elements (i.e. whether its size is 0).

@liveexample{The following code uses empty() to check if a JSON object contains any elements.,empty}

@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their empty() functions have constant complexity.

@iterators No changes.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of begin() == end().

See also

size() &#8212; returns the number of elements

Since

version 1.0.0

Note

This function does not return whether a string stored as JSON value is empty - it returns whether the JSON container itself is empty which is false in the case of a string.

Returns:

The return value depends on the different types and is defined as follows:

Value type	return value
null	true
boolean	false
string	false
number	false
object	result of function object_t::empty()
array	result of function array_t::empty()

inline size_type size() const noexcept

returns the number of elements

Returns the number of elements in a JSON value.

@liveexample{The following code calls size() on the different value types.,size}

@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their size() functions have constant complexity.

@iterators No changes.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of std::distance(begin(), end()).

See also

empty() &#8212; checks whether the container is empty

See also

max_size() &#8212; returns the maximal number of elements

Since

version 1.0.0

Note

This function does not return the length of a string stored as JSON value - it returns the number of elements in the JSON value which is 1 in the case of a string.

Returns:

The return value depends on the different types and is defined as follows:

Value type	return value
null	0
boolean	1
string	1
number	1
object	result of function object_t::size()
array	result of function array_t::size()

inline size_type max_size() const noexcept

returns the maximum possible number of elements

Returns the maximum number of elements a JSON value is able to hold due to system or library implementation limitations, i.e. std::distance(begin(), end()) for the JSON value.

@liveexample{The following code calls max_size() on the different value types. Note the output is implementation specific.,max_size}

@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their max_size() functions have constant complexity.

@iterators No changes.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of returning b.size() where b is the largest possible JSON value.

See also

size() &#8212; returns the number of elements

Since

version 1.0.0

Returns:

The return value depends on the different types and is defined as follows:

Value type	return value
null	0 (same as size())
boolean	1 (same as size())
string	1 (same as size())
number	1 (same as size())
object	result of function object_t::max_size()
array	result of function array_t::max_size()

inline bool empty() const noexcept

checks whether the container is empty.

Checks if a JSON value has no elements (i.e. whether its size is 0).

@liveexample{The following code uses empty() to check if a JSON object contains any elements.,empty}

@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their empty() functions have constant complexity.

@iterators No changes.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of begin() == end().

See also

size() &#8212; returns the number of elements

Since

version 1.0.0

Note

This function does not return whether a string stored as JSON value is empty - it returns whether the JSON container itself is empty which is false in the case of a string.

Returns:

The return value depends on the different types and is defined as follows:

Value type	return value
null	true
boolean	false
string	false
number	false
binary	false
object	result of function object_t::empty()
array	result of function array_t::empty()

inline size_type size() const noexcept

returns the number of elements

Returns the number of elements in a JSON value.

@liveexample{The following code calls size() on the different value types.,size}

@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their size() functions have constant complexity.

@iterators No changes.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of std::distance(begin(), end()).

See also

empty() &#8212; checks whether the container is empty

See also

max_size() &#8212; returns the maximal number of elements

Since

version 1.0.0

Note

This function does not return the length of a string stored as JSON value - it returns the number of elements in the JSON value which is 1 in the case of a string.

Returns:

The return value depends on the different types and is defined as follows:

Value type	return value
null	0
boolean	1
string	1
number	1
binary	1
object	result of function object_t::size()
array	result of function array_t::size()

inline size_type max_size() const noexcept

returns the maximum possible number of elements

Returns the maximum number of elements a JSON value is able to hold due to system or library implementation limitations, i.e. std::distance(begin(), end()) for the JSON value.

@liveexample{The following code calls max_size() on the different value types. Note the output is implementation specific.,max_size}

@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their max_size() functions have constant complexity.

@iterators No changes.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@requirement This function helps basic_json satisfying the Container requirements:

• The complexity is constant.

• Has the semantics of returning b.size() where b is the largest possible JSON value.

See also

size() &#8212; returns the number of elements

Since

version 1.0.0

Returns:

The return value depends on the different types and is defined as follows:

Value type	return value
null	0 (same as size())
boolean	1 (same as size())
string	1 (same as size())
number	1 (same as size())
binary	1 (same as size())
object	result of function object_t::max_size()
array	result of function array_t::max_size()

JSON Pointer functions

inline reference operator[](const json_pointer &ptr)

access specified element via JSON Pointer

Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. Similar to

operator[](const typename

, null values are created in arrays and objects if necessary.

In particular:

• If the JSON pointer points to an object key that does not exist, it is created an filled with a null value before a reference to it is returned.

• If the JSON pointer points to an array index that does not exist, it is created an filled with a null value before a reference to it is returned. All indices between the current maximum and the given index are also filled with null.

• The special value - is treated as a synonym for the index past the end.

@complexity Constant.

@liveexample{The behavior is shown in the example.,operatorjson_pointer}

Since

version 2.0.0

Parameters:

ptr – [in] a JSON pointer

Returns:

reference to the element pointed to by ptr

Throws:

• parse_error.106 – if an array index begins with ‘0’

• parse_error.109 – if an array index was not a number

• out_of_range.404 – if the JSON pointer can not be resolved

inline const_reference operator[](const json_pointer &ptr) const

access specified element via JSON Pointer

Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. The function does not change the JSON value; no null values are created. In particular, the the special value - yields an exception.

@complexity Constant.

@liveexample{The behavior is shown in the example.,operatorjson_pointer_const}

Since

version 2.0.0

Parameters:

ptr – [in] JSON pointer to the desired element

Returns:

const reference to the element pointed to by ptr

Throws:

• parse_error.106 – if an array index begins with ‘0’

• parse_error.109 – if an array index was not a number

• out_of_range.402 – if the array index ‘-’ is used

• out_of_range.404 – if the JSON pointer can not be resolved

inline reference at(const json_pointer &ptr)

access specified element via JSON Pointer

Returns a reference to the element at with specified JSON pointer ptr, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The behavior is shown in the example.,at_json_pointer}

Since

version 2.0.0

Parameters:

ptr – [in] JSON pointer to the desired element

Throws:

• parse_error.106 – if an array index in the passed JSON pointer ptr begins with ‘0’. See example below.

• parse_error.109 – if an array index in the passed JSON pointer ptr is not a number. See example below.

• out_of_range.401 – if an array index in the passed JSON pointer ptr is out of range. See example below.

• out_of_range.402 – if the array index ‘-’ is used in the passed JSON pointer ptr. As at provides checked access (and no elements are implicitly inserted), the index ‘-’ is always invalid. See example below.

• out_of_range.403 – if the JSON pointer describes a key of an object which cannot be found. See example below.

• out_of_range.404 – if the JSON pointer ptr can not be resolved. See example below.

Returns:

reference to the element pointed to by ptr

inline const_reference at(const json_pointer &ptr) const

access specified element via JSON Pointer

Returns a const reference to the element at with specified JSON pointer ptr, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The behavior is shown in the example.,at_json_pointer_const}

Since

version 2.0.0

Parameters:

ptr – [in] JSON pointer to the desired element

Throws:

• parse_error.106 – if an array index in the passed JSON pointer ptr begins with ‘0’. See example below.

• parse_error.109 – if an array index in the passed JSON pointer ptr is not a number. See example below.

• out_of_range.401 – if an array index in the passed JSON pointer ptr is out of range. See example below.

• out_of_range.402 – if the array index ‘-’ is used in the passed JSON pointer ptr. As at provides checked access (and no elements are implicitly inserted), the index ‘-’ is always invalid. See example below.

• out_of_range.403 – if the JSON pointer describes a key of an object which cannot be found. See example below.

• out_of_range.404 – if the JSON pointer ptr can not be resolved. See example below.

Returns:

reference to the element pointed to by ptr

inline basic_json flatten() const

return flattened JSON value

The function creates a JSON object whose keys are JSON pointers (see RFC 6901) and whose values are all primitive. The original JSON value can be restored using the unflatten() function.

@complexity Linear in the size the JSON value.

@liveexample{The following code shows how a JSON object is flattened to an object whose keys consist of JSON pointers.,flatten}

See also

unflatten() for the reverse function

Since

version 2.0.0

Note

Empty objects and arrays are flattened to null and will not be reconstructed correctly by the unflatten() function.

Returns:

an object that maps JSON pointers to primitive values

inline basic_json unflatten() const

unflatten a previously flattened JSON value

The function restores the arbitrary nesting of a JSON value that has been flattened before using the flatten() function. The JSON value must meet certain constraints:

1. The value must be an object.

2. The keys must be JSON pointers (see RFC 6901)

3. The mapped values must be primitive JSON types.

@complexity Linear in the size the JSON value.

@liveexample{The following code shows how a flattened JSON object is unflattened into the original nested JSON object.,unflatten}

See also

flatten() for the reverse function

Since

version 2.0.0

Note

Empty objects and arrays are flattened by flatten() to null values and can not unflattened to their original type. Apart from this example, for a JSON value j, the following is always true: j == j.flatten().unflatten().

Returns:

the original JSON from a flattened version

Throws:

• type_error.314 – if value is not an object

• type_error.315 – if object values are not primitive

inline reference operator[](const json_pointer &ptr)

access specified element via JSON Pointer

Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. Similar to

operator[](const typename

, null values are created in arrays and objects if necessary.

In particular:

• If the JSON pointer points to an object key that does not exist, it is created an filled with a null value before a reference to it is returned.

• If the JSON pointer points to an array index that does not exist, it is created an filled with a null value before a reference to it is returned. All indices between the current maximum and the given index are also filled with null.

• The special value - is treated as a synonym for the index past the end.

@complexity Constant.

@liveexample{The behavior is shown in the example.,operatorjson_pointer}

Since

version 2.0.0

Parameters:

ptr – [in] a JSON pointer

Returns:

reference to the element pointed to by ptr

Throws:

• parse_error.106 – if an array index begins with ‘0’

• parse_error.109 – if an array index was not a number

• out_of_range.404 – if the JSON pointer can not be resolved

inline const_reference operator[](const json_pointer &ptr) const

access specified element via JSON Pointer

Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. The function does not change the JSON value; no null values are created. In particular, the special value - yields an exception.

@complexity Constant.

@liveexample{The behavior is shown in the example.,operatorjson_pointer_const}

Since

version 2.0.0

Parameters:

ptr – [in] JSON pointer to the desired element

Returns:

const reference to the element pointed to by ptr

Throws:

• parse_error.106 – if an array index begins with ‘0’

• parse_error.109 – if an array index was not a number

• out_of_range.402 – if the array index ‘-’ is used

• out_of_range.404 – if the JSON pointer can not be resolved

inline reference at(const json_pointer &ptr)

access specified element via JSON Pointer

Returns a reference to the element at with specified JSON pointer ptr, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The behavior is shown in the example.,at_json_pointer}

Since

version 2.0.0

Parameters:

ptr – [in] JSON pointer to the desired element

Throws:

• parse_error.106 – if an array index in the passed JSON pointer ptr begins with ‘0’. See example below.

• parse_error.109 – if an array index in the passed JSON pointer ptr is not a number. See example below.

• out_of_range.401 – if an array index in the passed JSON pointer ptr is out of range. See example below.

• out_of_range.402 – if the array index ‘-’ is used in the passed JSON pointer ptr. As at provides checked access (and no elements are implicitly inserted), the index ‘-’ is always invalid. See example below.

• out_of_range.403 – if the JSON pointer describes a key of an object which cannot be found. See example below.

• out_of_range.404 – if the JSON pointer ptr can not be resolved. See example below.

Returns:

reference to the element pointed to by ptr

inline const_reference at(const json_pointer &ptr) const

access specified element via JSON Pointer

Returns a const reference to the element at with specified JSON pointer ptr, with bounds checking.

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

@complexity Constant.

@liveexample{The behavior is shown in the example.,at_json_pointer_const}

Since

version 2.0.0

Parameters:

ptr – [in] JSON pointer to the desired element

Throws:

• parse_error.106 – if an array index in the passed JSON pointer ptr begins with ‘0’. See example below.

• parse_error.109 – if an array index in the passed JSON pointer ptr is not a number. See example below.

• out_of_range.401 – if an array index in the passed JSON pointer ptr is out of range. See example below.

• out_of_range.402 – if the array index ‘-’ is used in the passed JSON pointer ptr. As at provides checked access (and no elements are implicitly inserted), the index ‘-’ is always invalid. See example below.

• out_of_range.403 – if the JSON pointer describes a key of an object which cannot be found. See example below.

• out_of_range.404 – if the JSON pointer ptr can not be resolved. See example below.

Returns:

reference to the element pointed to by ptr

inline basic_json flatten() const

return flattened JSON value

The function creates a JSON object whose keys are JSON pointers (see RFC 6901) and whose values are all primitive. The original JSON value can be restored using the unflatten() function.

@complexity Linear in the size the JSON value.

@liveexample{The following code shows how a JSON object is flattened to an object whose keys consist of JSON pointers.,flatten}

See also

unflatten() for the reverse function

Since

version 2.0.0

Note

Empty objects and arrays are flattened to null and will not be reconstructed correctly by the unflatten() function.

Returns:

an object that maps JSON pointers to primitive values

inline basic_json unflatten() const

unflatten a previously flattened JSON value

The function restores the arbitrary nesting of a JSON value that has been flattened before using the flatten() function. The JSON value must meet certain constraints:

1. The value must be an object.

2. The keys must be JSON pointers (see RFC 6901)

3. The mapped values must be primitive JSON types.

@complexity Linear in the size the JSON value.

@liveexample{The following code shows how a flattened JSON object is unflattened into the original nested JSON object.,unflatten}

See also

flatten() for the reverse function

Since

version 2.0.0

Note

Empty objects and arrays are flattened by flatten() to null values and can not unflattened to their original type. Apart from this example, for a JSON value j, the following is always true: j == j.flatten().unflatten().

Returns:

the original JSON from a flattened version

Throws:

• type_error.314 – if value is not an object

• type_error.315 – if object values are not primitive

JSON Merge Patch functions

inline void merge_patch(const basic_json &apply_patch)

applies a JSON Merge Patch

The merge patch format is primarily intended for use with the HTTP PATCH method as a means of describing a set of modifications to a target resource’s content. This function applies a merge patch to the current JSON value.

The function implements the following algorithm from Section 2 of RFC 7396 (JSON Merge Patch):

define MergePatch(Target, Patch):
  if Patch is an Object:
    if Target is not an Object:
      Target = {} // Ignore the contents and set it to an empty Object
    for each Name/Value pair in Patch:
      if Value is null:
        if Name exists in Target:
          remove the Name/Value pair from Target
      else:
        Target[Name] = MergePatch(Target[Name], Value)
    return Target
  else:
    return Patch

Thereby, Target is the current object; that is, the patch is applied to the current value.

@complexity Linear in the lengths of patch.

@liveexample{The following code shows how a JSON Merge Patch is applied to a JSON document.,merge_patch}

See also

patch &#8212; apply a JSON patch

See also

RFC 7396 (JSON Merge Patch)

Since

version 3.0.0

Parameters:

apply_patch – [in] the patch to apply

inline void merge_patch(const basic_json &apply_patch)

applies a JSON Merge Patch

The merge patch format is primarily intended for use with the HTTP PATCH method as a means of describing a set of modifications to a target resource’s content. This function applies a merge patch to the current JSON value.

The function implements the following algorithm from Section 2 of RFC 7396 (JSON Merge Patch):

define MergePatch(Target, Patch):
  if Patch is an Object:
    if Target is not an Object:
      Target = {} // Ignore the contents and set it to an empty Object
    for each Name/Value pair in Patch:
      if Value is null:
        if Name exists in Target:
          remove the Name/Value pair from Target
      else:
        Target[Name] = MergePatch(Target[Name], Value)
    return Target
  else:
    return Patch

Thereby, Target is the current object; that is, the patch is applied to the current value.

@complexity Linear in the lengths of patch.

@liveexample{The following code shows how a JSON Merge Patch is applied to a JSON document.,merge_patch}

See also

patch &#8212; apply a JSON patch

See also

RFC 7396 (JSON Merge Patch)

Since

version 3.0.0

Parameters:

apply_patch – [in] the patch to apply

Public Types

using value_t = detail::value_t

using json_pointer = ::nlohmann::json_pointer<basic_json>

JSON Pointer, see nlohmann::json_pointer.

template<typename T, typename SFINAE>
using json_serializer = JSONSerializer<T, SFINAE>

using error_handler_t = detail::error_handler_t

how to treat decoding errors

using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>

helper type for initializer lists of basic_json values

using input_format_t = detail::input_format_t

using json_sax_t = json_sax<basic_json>

SAX interface type, see nlohmann::json_sax.

using parse_event_t = typename parser::parse_event_t

parser event types

The parser callback distinguishes the following events:

• object_start: the parser read { and started to process a JSON object

• key: the parser read a key of a value in an object

• object_end: the parser read } and finished processing a JSON object

• array_start: the parser read [ and started to process a JSON array

• array_end: the parser read ] and finished processing a JSON array

• value: the parser finished reading a JSON value

See also

parser_callback_t for more information and examples

using parser_callback_t = typename parser::parser_callback_t

per-element parser callback type

With a parser callback function, the result of parsing a JSON text can be influenced. When passed to parse, it is called on certain events (passed as parse_event_t via parameter event) with a set recursion depth depth and context JSON value parsed. The return value of the callback function is a boolean indicating whether the element that emitted the callback shall be kept or not.

We distinguish six scenarios (determined by the event type) in which the callback function can be called. The following table describes the values of the parameters depth, event, and parsed.

parameter event	description	parameter depth	parameter parsed
parse_event_t::object_start	the parser read { and started to process a JSON object	depth of the parent of the JSON object	a JSON value with type discarded
parse_event_t::key	the parser read a key of a value in an object	depth of the currently parsed JSON object	a JSON string containing the key
parse_event_t::object_end	the parser read } and finished processing a JSON object	depth of the parent of the JSON object	the parsed JSON object
parse_event_t::array_start	the parser read [ and started to process a JSON array	depth of the parent of the JSON array	a JSON value with type discarded
parse_event_t::array_end	the parser read ] and finished processing a JSON array	depth of the parent of the JSON array	the parsed JSON array
parse_event_t::value	the parser finished reading a JSON value	depth of the value	the parsed JSON value

Discarding a value (i.e., returning false) has different effects depending on the context in which function was called:

• Discarded values in structured types are skipped. That is, the parser will behave as if the discarded value was never read.

• In case a value outside a structured type is skipped, it is replaced with null. This case happens if the top-level element is skipped.

See also

parse for examples

Since

version 1.0.0

Param depth:

[in] the depth of the recursion during parsing

Param event:

[in] an event of type parse_event_t indicating the context in the callback function has been called

Param parsed:

[inout] the current intermediate parse result; note that writing to this value has no effect for parse_event_t::key events

Return:

Whether the JSON value which called the function during parsing should be kept (true) or not (false). In the latter case, it is either skipped completely or replaced by an empty discarded object.

using value_t = detail::value_t

using json_pointer = ::nlohmann::json_pointer<basic_json>

JSON Pointer, see nlohmann::json_pointer.

template<typename T, typename SFINAE>
using json_serializer = JSONSerializer<T, SFINAE>

using error_handler_t = detail::error_handler_t

how to treat decoding errors

using cbor_tag_handler_t = detail::cbor_tag_handler_t

how to treat CBOR tags

using initializer_list_t = std::initializer_list<detail::json_ref<basic_json>>

helper type for initializer lists of basic_json values

using input_format_t = detail::input_format_t

using json_sax_t = json_sax<basic_json>

SAX interface type, see nlohmann::json_sax.

using parse_event_t = detail::parse_event_t

parser event types

The parser callback distinguishes the following events:

• object_start: the parser read { and started to process a JSON object

• key: the parser read a key of a value in an object

• object_end: the parser read } and finished processing a JSON object

• array_start: the parser read [ and started to process a JSON array

• array_end: the parser read ] and finished processing a JSON array

• value: the parser finished reading a JSON value

See also

parser_callback_t for more information and examples

using parser_callback_t = detail::parser_callback_t<basic_json>

per-element parser callback type

With a parser callback function, the result of parsing a JSON text can be influenced. When passed to parse, it is called on certain events (passed as parse_event_t via parameter event) with a set recursion depth depth and context JSON value parsed. The return value of the callback function is a boolean indicating whether the element that emitted the callback shall be kept or not.

We distinguish six scenarios (determined by the event type) in which the callback function can be called. The following table describes the values of the parameters depth, event, and parsed.

parameter event	description	parameter depth	parameter parsed
parse_event_t::object_start	the parser read { and started to process a JSON object	depth of the parent of the JSON object	a JSON value with type discarded
parse_event_t::key	the parser read a key of a value in an object	depth of the currently parsed JSON object	a JSON string containing the key
parse_event_t::object_end	the parser read } and finished processing a JSON object	depth of the parent of the JSON object	the parsed JSON object
parse_event_t::array_start	the parser read [ and started to process a JSON array	depth of the parent of the JSON array	a JSON value with type discarded
parse_event_t::array_end	the parser read ] and finished processing a JSON array	depth of the parent of the JSON array	the parsed JSON array
parse_event_t::value	the parser finished reading a JSON value	depth of the value	the parsed JSON value

Discarding a value (i.e., returning false) has different effects depending on the context in which function was called:

• Discarded values in structured types are skipped. That is, the parser will behave as if the discarded value was never read.

• In case a value outside a structured type is skipped, it is replaced with null. This case happens if the top-level element is skipped.

See also

parse for examples

Since

version 1.0.0

Param depth:

[in] the depth of the recursion during parsing

Param event:

[in] an event of type parse_event_t indicating the context in the callback function has been called

Param parsed:

[inout] the current intermediate parse result; note that writing to this value has no effect for parse_event_t::key events

Return:

Whether the JSON value which called the function during parsing should be kept (true) or not (false). In the latter case, it is either skipped completely or replaced by an empty discarded object.

Public Functions

inline JSON_HEDLEY_RETURNS_NON_NULL const char * type_name () const noexcept

return the type as string

Returns the type name as string to be used in error messages - usually to indicate that a function was called on a wrong JSON type.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Constant.

@liveexample{The following code exemplifies type_name() for all JSON types.,type_name}

See also

type() &#8212; return the type of the JSON value

See also

operator value_t() &#8212; return the type of the JSON value (implicit)

Since

version 1.0.0, public since 2.1.0, const char* and noexcept since 3.0.0

Returns:

a string representation of a the m_type member:

Value type	return value
null	"null"
boolean	"boolean"
string	"string"
number	"number" (for all number types)
object	"object"
array	"array"
discarded	"discarded"

inline JSON_HEDLEY_RETURNS_NON_NULL const char * type_name () const noexcept

return the type as string

Returns the type name as string to be used in error messages - usually to indicate that a function was called on a wrong JSON type.

@exceptionsafety No-throw guarantee: this function never throws exceptions.

@complexity Constant.

@liveexample{The following code exemplifies type_name() for all JSON types.,type_name}

See also

type() &#8212; return the type of the JSON value

See also

operator value_t() &#8212; return the type of the JSON value (implicit)

Since

version 1.0.0, public since 2.1.0, const char* and noexcept since 3.0.0

Returns:

a string representation of a the m_type member:

Value type	return value
null	"null"
boolean	"boolean"
string	"string"
number	"number" (for all number types)
object	"object"
array	"array"
binary	"binary"
discarded	"discarded"

Public Static Functions

static inline allocator_type get_allocator()

returns the allocator associated with the container

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json meta ()

returns version information on the library

This function returns a JSON object with information about the library, including the version number and information on the platform and compiler.

@liveexample{The following code shows an example output of the meta() function.,meta}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@complexity Constant.

Since

2.1.0

Returns:

JSON object holding version information

key	description
compiler	Information on the used compiler. It is an object with the following keys: c++ (the used C++ standard), family (the compiler family; possible values are clang, icc, gcc, ilecpp, msvc, pgcpp, sunpro, and unknown), and version (the compiler version).
copyright	The copyright line for the library as string.
name	The name of the library as string.
platform	The used platform as string. Possible values are win32, linux, apple, unix, and unknown.
url	The URL of the project as string.
version	The version of the library. It is an object with the following keys: major, minor, and patch as defined by Semantic Versioning, and string (the version string).

static inline allocator_type get_allocator()

returns the allocator associated with the container

static inline JSON_HEDLEY_WARN_UNUSED_RESULT basic_json meta ()

returns version information on the library

This function returns a JSON object with information about the library, including the version number and information on the platform and compiler.

@liveexample{The following code shows an example output of the meta() function.,meta}

@exceptionsafety Strong guarantee: if an exception is thrown, there are no changes to any JSON value.

@complexity Constant.

Since

2.1.0

Returns:

JSON object holding version information

key	description
compiler	Information on the used compiler. It is an object with the following keys: c++ (the used C++ standard), family (the compiler family; possible values are clang, icc, gcc, ilecpp, msvc, pgcpp, sunpro, and unknown), and version (the compiler version).
copyright	The copyright line for the library as string.
name	The name of the library as string.
platform	The used platform as string. Possible values are win32, linux, apple, unix, and unknown.
url	The URL of the project as string.
version	The version of the library. It is an object with the following keys: major, minor, and patch as defined by Semantic Versioning, and string (the version string).

Friends

friend struct detail::external_constructor

friend class ::nlohmann::detail::iter_impl

friend class ::nlohmann::detail::binary_writer

friend class ::nlohmann::detail::binary_reader

friend class ::nlohmann::detail::json_sax_dom_parser

friend class ::nlohmann::detail::json_sax_dom_callback_parser

friend class ::nlohmann::detail::parser