asio::read_at

Attempt to read a certain amount of data at the specified offset before returning. More...

Functions
template<typename SyncRandomAccessReadDevice , typename MutableBufferSequence >
std::size_t	asio::read_at (SyncRandomAccessReadDevice &d, boost::uint64_t offset, const MutableBufferSequence &buffers)
template<typename SyncRandomAccessReadDevice , typename MutableBufferSequence , typename CompletionCondition >
std::size_t	asio::read_at (SyncRandomAccessReadDevice &d, boost::uint64_t offset, const MutableBufferSequence &buffers, CompletionCondition completion_condition)
template<typename SyncRandomAccessReadDevice , typename MutableBufferSequence , typename CompletionCondition >
std::size_t	asio::read_at (SyncRandomAccessReadDevice &d, boost::uint64_t offset, const MutableBufferSequence &buffers, CompletionCondition completion_condition, asio::error_code &ec)
template<typename SyncRandomAccessReadDevice , typename Allocator >
std::size_t	asio::read_at (SyncRandomAccessReadDevice &d, boost::uint64_t offset, basic_streambuf< Allocator > &b)
template<typename SyncRandomAccessReadDevice , typename Allocator , typename CompletionCondition >
std::size_t	asio::read_at (SyncRandomAccessReadDevice &d, boost::uint64_t offset, basic_streambuf< Allocator > &b, CompletionCondition completion_condition)
template<typename SyncRandomAccessReadDevice , typename Allocator , typename CompletionCondition >
std::size_t	asio::read_at (SyncRandomAccessReadDevice &d, boost::uint64_t offset, basic_streambuf< Allocator > &b, CompletionCondition completion_condition, asio::error_code &ec)

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Detailed Description

Attempt to read a certain amount of data at the specified offset before returning.

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Function Documentation

template<typename SyncRandomAccessReadDevice , typename MutableBufferSequence >

std::size_t asio::read_at	(	SyncRandomAccessReadDevice &	d,
		boost::uint64_t	offset,
		const MutableBufferSequence &	buffers
	)

Attempt to read a certain amount of data at the specified offset before returning. This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true:

• The supplied buffers are full. That is, the bytes transferred is equal to the sum of the buffer sizes.

• An error occurred.

This operation is implemented in terms of one or more calls to the device's read_some_at function.

Parameters:

d	The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept.
offset	The offset at which the data will be read.
buffers	One or more buffers into which the data will be read. The sum of the buffer sizes indicates the maximum number of bytes to read from the device.

Returns:

The number of bytes transferred.

Exceptions:

asio::system_error

Thrown on failure.

Example

To read into a single data buffer use the asio::buffer function as follows:

 asio::read_at(d, 42, asio::buffer(data, size)); 

See the asio::buffer documentation for information on reading into multiple buffers in one go, and how to use it with arrays, boost::array or std::vector.

Note:

This overload is equivalent to calling:

 asio::read_at(
     d, 42, buffers,
     asio::transfer_all()); 

template<typename SyncRandomAccessReadDevice , typename MutableBufferSequence , typename CompletionCondition >

std::size_t asio::read_at	(	SyncRandomAccessReadDevice &	d,
		boost::uint64_t	offset,
		const MutableBufferSequence &	buffers,
		CompletionCondition	completion_condition
	)

Attempt to read a certain amount of data at the specified offset before returning. This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true:

• The supplied buffers are full. That is, the bytes transferred is equal to the sum of the buffer sizes.

• The completion_condition function object returns true.

This operation is implemented in terms of one or more calls to the device's read_some_at function.

Parameters:

d	The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept.
offset	The offset at which the data will be read.
buffers	One or more buffers into which the data will be read. The sum of the buffer sizes indicates the maximum number of bytes to read from the device.
completion_condition	The function object to be called to determine whether the read operation is complete. The signature of the function object must be: bool completion_condition( // Result of latest read_some_at operation. const asio::error_code& error, // Number of bytes transferred so far. std::size_t bytes_transferred ); A return value of true indicates that the read operation is complete. False indicates that further calls to the device's read_some_at function are required.

Returns:

The number of bytes transferred.

Exceptions:

asio::system_error

Thrown on failure.

Example

To read into a single data buffer use the asio::buffer function as follows:

 asio::read_at(d, 42, asio::buffer(data, size),
     asio::transfer_at_least(32)); 

See the asio::buffer documentation for information on reading into multiple buffers in one go, and how to use it with arrays, boost::array or std::vector.

template<typename SyncRandomAccessReadDevice , typename MutableBufferSequence , typename CompletionCondition >

std::size_t asio::read_at	(	SyncRandomAccessReadDevice &	d,
		boost::uint64_t	offset,
		const MutableBufferSequence &	buffers,
		CompletionCondition	completion_condition,
		asio::error_code &	ec
	)

Attempt to read a certain amount of data at the specified offset before returning. This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true:

• The supplied buffers are full. That is, the bytes transferred is equal to the sum of the buffer sizes.

• The completion_condition function object returns true.

This operation is implemented in terms of one or more calls to the device's read_some_at function.

Parameters:

d	The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept.
offset	The offset at which the data will be read.
buffers	One or more buffers into which the data will be read. The sum of the buffer sizes indicates the maximum number of bytes to read from the device.
completion_condition	The function object to be called to determine whether the read operation is complete. The signature of the function object must be: bool completion_condition( const asio::error_code& error, // Result of latest read_some_at // operation. std::size_t bytes_transferred // Number of bytes transferred // so far. ); A return value of true indicates that the read operation is complete. False indicates that further calls to the device's read_some_at function are required.
ec	Set to indicate what error occurred, if any.

Returns:

The number of bytes read. If an error occurs, returns the total number of bytes successfully transferred prior to the error.

template<typename SyncRandomAccessReadDevice , typename Allocator >

std::size_t asio::read_at	(	SyncRandomAccessReadDevice &	d,
		boost::uint64_t	offset,
		basic_streambuf< Allocator > &	b
	)

Attempt to read a certain amount of data at the specified offset before returning. This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true:

• An error occurred.

This operation is implemented in terms of one or more calls to the device's read_some_at function.

Parameters:

d	The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept.
offset	The offset at which the data will be read.
b	The basic_streambuf object into which the data will be read.

Returns:

The number of bytes transferred.

Exceptions:

asio::system_error

Thrown on failure.

Note:

This overload is equivalent to calling:

 asio::read_at(
     d, 42, b,
     asio::transfer_all()); 

template<typename SyncRandomAccessReadDevice , typename Allocator , typename CompletionCondition >

std::size_t asio::read_at	(	SyncRandomAccessReadDevice &	d,
		boost::uint64_t	offset,
		basic_streambuf< Allocator > &	b,
		CompletionCondition	completion_condition
	)

Attempt to read a certain amount of data at the specified offset before returning. This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true:

• The completion_condition function object returns true.

This operation is implemented in terms of one or more calls to the device's read_some_at function.

Parameters:

d	The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept.
offset	The offset at which the data will be read.
b	The basic_streambuf object into which the data will be read.
completion_condition	The function object to be called to determine whether the read operation is complete. The signature of the function object must be: bool completion_condition( // Result of latest read_some_at operation. const asio::error_code& error, // Number of bytes transferred so far. std::size_t bytes_transferred ); A return value of true indicates that the read operation is complete. False indicates that further calls to the device's read_some_at function are required.

Returns:

The number of bytes transferred.

Exceptions:

asio::system_error

Thrown on failure.

template<typename SyncRandomAccessReadDevice , typename Allocator , typename CompletionCondition >

std::size_t asio::read_at	(	SyncRandomAccessReadDevice &	d,
		boost::uint64_t	offset,
		basic_streambuf< Allocator > &	b,
		CompletionCondition	completion_condition,
		asio::error_code &	ec
	)

Attempt to read a certain amount of data at the specified offset before returning. This function is used to read a certain number of bytes of data from a random access device at the specified offset. The call will block until one of the following conditions is true:

• The completion_condition function object returns true.

This operation is implemented in terms of one or more calls to the device's read_some_at function.

Parameters:

d	The device from which the data is to be read. The type must support the SyncRandomAccessReadDevice concept.
offset	The offset at which the data will be read.
b	The basic_streambuf object into which the data will be read.
completion_condition	The function object to be called to determine whether the read operation is complete. The signature of the function object must be: bool completion_condition( // Result of latest read_some_at operation. const asio::error_code& error, // Number of bytes transferred so far. std::size_t bytes_transferred ); A return value of true indicates that the read operation is complete. False indicates that further calls to the device's read_some_at function are required.
ec	Set to indicate what error occurred, if any.

Returns:

The number of bytes read. If an error occurs, returns the total number of bytes successfully transferred prior to the error.