gtest/include/gtest/gtest-printers.h

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//
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Author: wan@google.com (Zhanyong Wan)

// Google Test - The Google C++ Testing Framework
//
// This file implements a universal value printer that can print a
// value of any type T:
//
//   void ::testing::internal::UniversalPrinter<T>::Print(value, ostream_ptr);
//
// A user can teach this function how to print a class type T by
// defining either operator<<() or PrintTo() in the namespace that
// defines T.  More specifically, the FIRST defined function in the
// following list will be used (assuming T is defined in namespace
// foo):
//
//   1. foo::PrintTo(const T&, ostream*)
//   2. operator<<(ostream&, const T&) defined in either foo or the
//      global namespace.
//
// If none of the above is defined, it will print the debug string of
// the value if it is a protocol buffer, or print the raw bytes in the
// value otherwise.
//
// To aid debugging: when T is a reference type, the address of the
// value is also printed; when T is a (const) char pointer, both the
// pointer value and the NUL-terminated string it points to are
// printed.
//
// We also provide some convenient wrappers:
//
//   // Prints a value to a string.  For a (const or not) char
//   // pointer, the NUL-terminated string (but not the pointer) is
//   // printed.
//   std::string ::testing::PrintToString(const T& value);
//
//   // Prints a value tersely: for a reference type, the referenced
//   // value (but not the address) is printed; for a (const or not) char
//   // pointer, the NUL-terminated string (but not the pointer) is
//   // printed.
//   void ::testing::internal::UniversalTersePrint(const T& value, ostream*);
//
//   // Prints value using the type inferred by the compiler.  The difference
//   // from UniversalTersePrint() is that this function prints both the
//   // pointer and the NUL-terminated string for a (const or not) char pointer.
//   void ::testing::internal::UniversalPrint(const T& value, ostream*);
//
//   // Prints the fields of a tuple tersely to a string vector, one
//   // element for each field. Tuple support must be enabled in
//   // gtest-port.h.
//   std::vector<string> UniversalTersePrintTupleFieldsToStrings(
//       const Tuple& value);
//
// Known limitation:
//
// The print primitives print the elements of an STL-style container
// using the compiler-inferred type of *iter where iter is a
// const_iterator of the container.  When const_iterator is an input
// iterator but not a forward iterator, this inferred type may not
// match value_type, and the print output may be incorrect.  In
// practice, this is rarely a problem as for most containers
// const_iterator is a forward iterator.  We'll fix this if there's an
// actual need for it.  Note that this fix cannot rely on value_type
// being defined as many user-defined container types don't have
// value_type.

#ifndef GTEST_INCLUDE_GTEST_GTEST_PRINTERS_H_
#define GTEST_INCLUDE_GTEST_GTEST_PRINTERS_H_

#include <ostream>  // NOLINT
#include <sstream>
#include <string>
#include <utility>
#include <vector>
#include "gtest/internal/gtest-port.h"
#include "gtest/internal/gtest-internal.h"

namespace testing
{

// Definitions in the 'internal' and 'internal2' name spaces are
// subject to change without notice.  DO NOT USE THEM IN USER CODE!
namespace internal2
{

// Prints the given number of bytes in the given object to the given
// ostream.
GTEST_API_ void PrintBytesInObjectTo(const unsigned char * obj_bytes,
                                     size_t count,
                                     ::std::ostream * os);

// For selecting which printer to use when a given type has neither <<
// nor PrintTo().
enum TypeKind
{
  kProtobuf,              // a protobuf type
  kConvertibleToInteger,  // a type implicitly convertible to BiggestInt
  // (e.g. a named or unnamed enum type)
  kOtherType              // anything else
};

// TypeWithoutFormatter<T, kTypeKind>::PrintValue(value, os) is called
// by the universal printer to print a value of type T when neither
// operator<< nor PrintTo() is defined for T, where kTypeKind is the
// "kind" of T as defined by enum TypeKind.
template <typename T, TypeKind kTypeKind>
class TypeWithoutFormatter
{
public:
  // This default version is called when kTypeKind is kOtherType.
  static void PrintValue(const T & value, ::std::ostream * os)
  {
    PrintBytesInObjectTo(reinterpret_cast<const unsigned char *>(&value),
                         sizeof(value), os);
  }
};

// We print a protobuf using its ShortDebugString() when the string
// doesn't exceed this many characters; otherwise we print it using
// DebugString() for better readability.
const size_t kProtobufOneLinerMaxLength = 50;

template <typename T>
class TypeWithoutFormatter<T, kProtobuf>
{
public:
  static void PrintValue(const T & value, ::std::ostream * os)
  {
    const ::testing::internal::string short_str = value.ShortDebugString();
    const ::testing::internal::string pretty_str =
      short_str.length() <= kProtobufOneLinerMaxLength ?
      short_str : ("\n" + value.DebugString());
    *os << ("<" + pretty_str + ">");
  }
};

template <typename T>
class TypeWithoutFormatter<T, kConvertibleToInteger>
{
public:
  // Since T has no << operator or PrintTo() but can be implicitly
  // converted to BiggestInt, we print it as a BiggestInt.
  //
  // Most likely T is an enum type (either named or unnamed), in which
  // case printing it as an integer is the desired behavior.  In case
  // T is not an enum, printing it as an integer is the best we can do
  // given that it has no user-defined printer.
  static void PrintValue(const T & value, ::std::ostream * os)
  {
    const internal::BiggestInt kBigInt = value;
    *os << kBigInt;
  }
};

// Prints the given value to the given ostream.  If the value is a
// protocol message, its debug string is printed; if it's an enum or
// of a type implicitly convertible to BiggestInt, it's printed as an
// integer; otherwise the bytes in the value are printed.  This is
// what UniversalPrinter<T>::Print() does when it knows nothing about
// type T and T has neither << operator nor PrintTo().
//
// A user can override this behavior for a class type Foo by defining
// a << operator in the namespace where Foo is defined.
//
// We put this operator in namespace 'internal2' instead of 'internal'
// to simplify the implementation, as much code in 'internal' needs to
// use << in STL, which would conflict with our own << were it defined
// in 'internal'.
//
// Note that this operator<< takes a generic std::basic_ostream<Char,
// CharTraits> type instead of the more restricted std::ostream.  If
// we define it to take an std::ostream instead, we'll get an
// "ambiguous overloads" compiler error when trying to print a type
// Foo that supports streaming to std::basic_ostream<Char,
// CharTraits>, as the compiler cannot tell whether
// operator<<(std::ostream&, const T&) or
// operator<<(std::basic_stream<Char, CharTraits>, const Foo&) is more
// specific.
template <typename Char, typename CharTraits, typename T>
::std::basic_ostream<Char, CharTraits> & operator<<(
  ::std::basic_ostream<Char, CharTraits> & os, const T & x)
{
  TypeWithoutFormatter < T,
                       (internal::IsAProtocolMessage<T>::value ? kProtobuf :
                        internal::ImplicitlyConvertible<const T &, internal::BiggestInt>::value ?
                        kConvertibleToInteger : kOtherType) >::PrintValue(x, &os);
  return os;
}

}  // namespace internal2
}  // namespace testing

// This namespace MUST NOT BE NESTED IN ::testing, or the name look-up
// magic needed for implementing UniversalPrinter won't work.
namespace testing_internal
{

// Used to print a value that is not an STL-style container when the
// user doesn't define PrintTo() for it.
template <typename T>
void DefaultPrintNonContainerTo(const T & value, ::std::ostream * os)
{
  // With the following statement, during unqualified name lookup,
  // testing::internal2::operator<< appears as if it was declared in
  // the nearest enclosing namespace that contains both
  // ::testing_internal and ::testing::internal2, i.e. the global
  // namespace.  For more details, refer to the C++ Standard section
  // 7.3.4-1 [namespace.udir].  This allows us to fall back onto
  // testing::internal2::operator<< in case T doesn't come with a <<
  // operator.
  //
  // We cannot write 'using ::testing::internal2::operator<<;', which
  // gcc 3.3 fails to compile due to a compiler bug.
  using namespace ::testing::internal2;  // NOLINT

  // Assuming T is defined in namespace foo, in the next statement,
  // the compiler will consider all of:
  //
  //   1. foo::operator<< (thanks to Koenig look-up),
  //   2. ::operator<< (as the current namespace is enclosed in ::),
  //   3. testing::internal2::operator<< (thanks to the using statement above).
  //
  // The operator<< whose type matches T best will be picked.
  //
  // We deliberately allow #2 to be a candidate, as sometimes it's
  // impossible to define #1 (e.g. when foo is ::std, defining
  // anything in it is undefined behavior unless you are a compiler
  // vendor.).
  *os << value;
}

}  // namespace testing_internal

namespace testing
{
namespace internal
{

// UniversalPrinter<T>::Print(value, ostream_ptr) prints the given
// value to the given ostream.  The caller must ensure that
// 'ostream_ptr' is not NULL, or the behavior is undefined.
//
// We define UniversalPrinter as a class template (as opposed to a
// function template), as we need to partially specialize it for
// reference types, which cannot be done with function templates.
template <typename T>
class UniversalPrinter;

template <typename T>
void UniversalPrint(const T & value, ::std::ostream * os);

// Used to print an STL-style container when the user doesn't define
// a PrintTo() for it.
template <typename C>
void DefaultPrintTo(IsContainer /* dummy */,
                    false_type /* is not a pointer */,
                    const C & container, ::std::ostream * os)
{
  const size_t kMaxCount = 32;  // The maximum number of elements to print.
  *os << '{';
  size_t count = 0;

  for (typename C::const_iterator it = container.begin();
       it != container.end(); ++it, ++count)
    {
      if (count > 0)
        {
          *os << ',';

          if (count == kMaxCount)    // Enough has been printed.
            {
              *os << " ...";
              break;
            }
        }

      *os << ' ';
      // We cannot call PrintTo(*it, os) here as PrintTo() doesn't
      // handle *it being a native array.
      internal::UniversalPrint(*it, os);
    }

  if (count > 0)
    {
      *os << ' ';
    }

  *os << '}';
}

// Used to print a pointer that is neither a char pointer nor a member
// pointer, when the user doesn't define PrintTo() for it.  (A member
// variable pointer or member function pointer doesn't really point to
// a location in the address space.  Their representation is
// implementation-defined.  Therefore they will be printed as raw
// bytes.)
template <typename T>
void DefaultPrintTo(IsNotContainer /* dummy */,
                    true_type /* is a pointer */,
                    T * p, ::std::ostream * os)
{
  if (p == NULL)
    {
      *os << "NULL";
    }

  else
    {
      // C++ doesn't allow casting from a function pointer to any object
      // pointer.
      //
      // IsTrue() silences warnings: "Condition is always true",
      // "unreachable code".
      if (IsTrue(ImplicitlyConvertible<T *, const void *>::value))
        {
          // T is not a function type.  We just call << to print p,
          // relying on ADL to pick up user-defined << for their pointer
          // types, if any.
          *os << p;
        }

      else
        {
          // T is a function type, so '*os << p' doesn't do what we want
          // (it just prints p as bool).  We want to print p as a const
          // void*.  However, we cannot cast it to const void* directly,
          // even using reinterpret_cast, as earlier versions of gcc
          // (e.g. 3.4.5) cannot compile the cast when p is a function
          // pointer.  Casting to UInt64 first solves the problem.
          *os << reinterpret_cast<const void *>(
                reinterpret_cast<internal::UInt64>(p));
        }
    }
}

// Used to print a non-container, non-pointer value when the user
// doesn't define PrintTo() for it.
template <typename T>
void DefaultPrintTo(IsNotContainer /* dummy */,
                    false_type /* is not a pointer */,
                    const T & value, ::std::ostream * os)
{
  ::testing_internal::DefaultPrintNonContainerTo(value, os);
}

// Prints the given value using the << operator if it has one;
// otherwise prints the bytes in it.  This is what
// UniversalPrinter<T>::Print() does when PrintTo() is not specialized
// or overloaded for type T.
//
// A user can override this behavior for a class type Foo by defining
// an overload of PrintTo() in the namespace where Foo is defined.  We
// give the user this option as sometimes defining a << operator for
// Foo is not desirable (e.g. the coding style may prevent doing it,
// or there is already a << operator but it doesn't do what the user
// wants).
template <typename T>
void PrintTo(const T & value, ::std::ostream * os)
{
  // DefaultPrintTo() is overloaded.  The type of its first two
  // arguments determine which version will be picked.  If T is an
  // STL-style container, the version for container will be called; if
  // T is a pointer, the pointer version will be called; otherwise the
  // generic version will be called.
  //
  // Note that we check for container types here, prior to we check
  // for protocol message types in our operator<<.  The rationale is:
  //
  // For protocol messages, we want to give people a chance to
  // override Google Mock's format by defining a PrintTo() or
  // operator<<.  For STL containers, other formats can be
  // incompatible with Google Mock's format for the container
  // elements; therefore we check for container types here to ensure
  // that our format is used.
  //
  // The second argument of DefaultPrintTo() is needed to bypass a bug
  // in Symbian's C++ compiler that prevents it from picking the right
  // overload between:
  //
  //   PrintTo(const T& x, ...);
  //   PrintTo(T* x, ...);
  DefaultPrintTo(IsContainerTest<T>(0), is_pointer<T>(), value, os);
}

// The following list of PrintTo() overloads tells
// UniversalPrinter<T>::Print() how to print standard types (built-in
// types, strings, plain arrays, and pointers).

// Overloads for various char types.
GTEST_API_ void PrintTo(unsigned char c, ::std::ostream * os);
GTEST_API_ void PrintTo(signed char c, ::std::ostream * os);
inline void PrintTo(char c, ::std::ostream * os)
{
  // When printing a plain char, we always treat it as unsigned.  This
  // way, the output won't be affected by whether the compiler thinks
  // char is signed or not.
  PrintTo(static_cast<unsigned char>(c), os);
}

// Overloads for other simple built-in types.
inline void PrintTo(bool x, ::std::ostream * os)
{
  *os << (x ? "true" : "false");
}

// Overload for wchar_t type.
// Prints a wchar_t as a symbol if it is printable or as its internal
// code otherwise and also as its decimal code (except for L'\0').
// The L'\0' char is printed as "L'\\0'". The decimal code is printed
// as signed integer when wchar_t is implemented by the compiler
// as a signed type and is printed as an unsigned integer when wchar_t
// is implemented as an unsigned type.
GTEST_API_ void PrintTo(wchar_t wc, ::std::ostream * os);

// Overloads for C strings.
GTEST_API_ void PrintTo(const char * s, ::std::ostream * os);
inline void PrintTo(char * s, ::std::ostream * os)
{
  PrintTo(ImplicitCast_<const char *>(s), os);
}

// signed/unsigned char is often used for representing binary data, so
// we print pointers to it as void* to be safe.
inline void PrintTo(const signed char * s, ::std::ostream * os)
{
  PrintTo(ImplicitCast_<const void *>(s), os);
}
inline void PrintTo(signed char * s, ::std::ostream * os)
{
  PrintTo(ImplicitCast_<const void *>(s), os);
}
inline void PrintTo(const unsigned char * s, ::std::ostream * os)
{
  PrintTo(ImplicitCast_<const void *>(s), os);
}
inline void PrintTo(unsigned char * s, ::std::ostream * os)
{
  PrintTo(ImplicitCast_<const void *>(s), os);
}

// MSVC can be configured to define wchar_t as a typedef of unsigned
// short.  It defines _NATIVE_WCHAR_T_DEFINED when wchar_t is a native
// type.  When wchar_t is a typedef, defining an overload for const
// wchar_t* would cause unsigned short* be printed as a wide string,
// possibly causing invalid memory accesses.
#if !defined(_MSC_VER) || defined(_NATIVE_WCHAR_T_DEFINED)
// Overloads for wide C strings
GTEST_API_ void PrintTo(const wchar_t * s, ::std::ostream * os);
inline void PrintTo(wchar_t * s, ::std::ostream * os)
{
  PrintTo(ImplicitCast_<const wchar_t *>(s), os);
}
#endif

// Overload for C arrays.  Multi-dimensional arrays are printed
// properly.

// Prints the given number of elements in an array, without printing
// the curly braces.
template <typename T>
void PrintRawArrayTo(const T a[], size_t count, ::std::ostream * os)
{
  UniversalPrint(a[0], os);

  for (size_t i = 1; i != count; i++)
    {
      *os << ", ";
      UniversalPrint(a[i], os);
    }
}

// Overloads for ::string and ::std::string.
#if GTEST_HAS_GLOBAL_STRING
GTEST_API_ void PrintStringTo(const ::string & s, ::std::ostream * os);
inline void PrintTo(const ::string & s, ::std::ostream * os)
{
  PrintStringTo(s, os);
}
#endif  // GTEST_HAS_GLOBAL_STRING

GTEST_API_ void PrintStringTo(const ::std::string & s, ::std::ostream * os);
inline void PrintTo(const ::std::string & s, ::std::ostream * os)
{
  PrintStringTo(s, os);
}

// Overloads for ::wstring and ::std::wstring.
#if GTEST_HAS_GLOBAL_WSTRING
GTEST_API_ void PrintWideStringTo(const ::wstring & s, ::std::ostream * os);
inline void PrintTo(const ::wstring & s, ::std::ostream * os)
{
  PrintWideStringTo(s, os);
}
#endif  // GTEST_HAS_GLOBAL_WSTRING

#if GTEST_HAS_STD_WSTRING
GTEST_API_ void PrintWideStringTo(const ::std::wstring & s, ::std::ostream * os);
inline void PrintTo(const ::std::wstring & s, ::std::ostream * os)
{
  PrintWideStringTo(s, os);
}
#endif  // GTEST_HAS_STD_WSTRING

#if GTEST_HAS_TR1_TUPLE
// Overload for ::std::tr1::tuple.  Needed for printing function arguments,
// which are packed as tuples.

// Helper function for printing a tuple.  T must be instantiated with
// a tuple type.
template <typename T>
void PrintTupleTo(const T & t, ::std::ostream * os);

// Overloaded PrintTo() for tuples of various arities.  We support
// tuples of up-to 10 fields.  The following implementation works
// regardless of whether tr1::tuple is implemented using the
// non-standard variadic template feature or not.

inline void PrintTo(const ::std::tr1::tuple<> & t, ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1>
void PrintTo(const ::std::tr1::tuple<T1> & t, ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2>
void PrintTo(const ::std::tr1::tuple<T1, T2> & t, ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3>
void PrintTo(const ::std::tr1::tuple<T1, T2, T3> & t, ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3, typename T4>
void PrintTo(const ::std::tr1::tuple<T1, T2, T3, T4> & t, ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3, typename T4, typename T5>
void PrintTo(const ::std::tr1::tuple<T1, T2, T3, T4, T5> & t,
             ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6>
void PrintTo(const ::std::tr1::tuple<T1, T2, T3, T4, T5, T6> & t,
             ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7>
void PrintTo(const ::std::tr1::tuple<T1, T2, T3, T4, T5, T6, T7> & t,
             ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8>
void PrintTo(const ::std::tr1::tuple<T1, T2, T3, T4, T5, T6, T7, T8> & t,
             ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9>
void PrintTo(const ::std::tr1::tuple<T1, T2, T3, T4, T5, T6, T7, T8, T9> & t,
             ::std::ostream * os)
{
  PrintTupleTo(t, os);
}

template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10>
void PrintTo(
  const ::std::tr1::tuple<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10> & t,
  ::std::ostream * os)
{
  PrintTupleTo(t, os);
}
#endif  // GTEST_HAS_TR1_TUPLE

// Overload for std::pair.
template <typename T1, typename T2>
void PrintTo(const ::std::pair<T1, T2> & value, ::std::ostream * os)
{
  *os << '(';
  // We cannot use UniversalPrint(value.first, os) here, as T1 may be
  // a reference type.  The same for printing value.second.
  UniversalPrinter<T1>::Print(value.first, os);
  *os << ", ";
  UniversalPrinter<T2>::Print(value.second, os);
  *os << ')';
}

// Implements printing a non-reference type T by letting the compiler
// pick the right overload of PrintTo() for T.
template <typename T>
class UniversalPrinter
{
public:
  // MSVC warns about adding const to a function type, so we want to
  // disable the warning.
#ifdef _MSC_VER
# pragma warning(push)          // Saves the current warning state.
# pragma warning(disable:4180)  // Temporarily disables warning 4180.
#endif  // _MSC_VER

  // Note: we deliberately don't call this PrintTo(), as that name
  // conflicts with ::testing::internal::PrintTo in the body of the
  // function.
  static void Print(const T & value, ::std::ostream * os)
  {
    // By default, ::testing::internal::PrintTo() is used for printing
    // the value.
    //
    // Thanks to Koenig look-up, if T is a class and has its own
    // PrintTo() function defined in its namespace, that function will
    // be visible here.  Since it is more specific than the generic ones
    // in ::testing::internal, it will be picked by the compiler in the
    // following statement - exactly what we want.
    PrintTo(value, os);
  }

#ifdef _MSC_VER
# pragma warning(pop)           // Restores the warning state.
#endif  // _MSC_VER
};

// UniversalPrintArray(begin, len, os) prints an array of 'len'
// elements, starting at address 'begin'.
template <typename T>
void UniversalPrintArray(const T * begin, size_t len, ::std::ostream * os)
{
  if (len == 0)
    {
      *os << "{}";
    }

  else
    {
      *os << "{ ";
      const size_t kThreshold = 18;
      const size_t kChunkSize = 8;

      // If the array has more than kThreshold elements, we'll have to
      // omit some details by printing only the first and the last
      // kChunkSize elements.
      // TODO(wan@google.com): let the user control the threshold using a flag.
      if (len <= kThreshold)
        {
          PrintRawArrayTo(begin, len, os);
        }

      else
        {
          PrintRawArrayTo(begin, kChunkSize, os);
          *os << ", ..., ";
          PrintRawArrayTo(begin + len - kChunkSize, kChunkSize, os);
        }

      *os << " }";
    }
}
// This overload prints a (const) char array compactly.
GTEST_API_ void UniversalPrintArray(
  const char * begin, size_t len, ::std::ostream * os);

// This overload prints a (const) wchar_t array compactly.
GTEST_API_ void UniversalPrintArray(
  const wchar_t * begin, size_t len, ::std::ostream * os);

// Implements printing an array type T[N].
template <typename T, size_t N>
class UniversalPrinter<T[N]>
{
public:
  // Prints the given array, omitting some elements when there are too
  // many.
  static void Print(const T(&a)[N], ::std::ostream * os)
  {
    UniversalPrintArray(a, N, os);
  }
};

// Implements printing a reference type T&.
template <typename T>
class UniversalPrinter<T &>
{
public:
  // MSVC warns about adding const to a function type, so we want to
  // disable the warning.
#ifdef _MSC_VER
# pragma warning(push)          // Saves the current warning state.
# pragma warning(disable:4180)  // Temporarily disables warning 4180.
#endif  // _MSC_VER

  static void Print(const T & value, ::std::ostream * os)
  {
    // Prints the address of the value.  We use reinterpret_cast here
    // as static_cast doesn't compile when T is a function type.
    *os << "@" << reinterpret_cast<const void *>(&value) << " ";

    // Then prints the value itself.
    UniversalPrint(value, os);
  }

#ifdef _MSC_VER
# pragma warning(pop)           // Restores the warning state.
#endif  // _MSC_VER
};

// Prints a value tersely: for a reference type, the referenced value
// (but not the address) is printed; for a (const) char pointer, the
// NUL-terminated string (but not the pointer) is printed.

template <typename T>
class UniversalTersePrinter
{
public:
  static void Print(const T & value, ::std::ostream * os)
  {
    UniversalPrint(value, os);
  }
};
template <typename T>
class UniversalTersePrinter<T &>
{
public:
  static void Print(const T & value, ::std::ostream * os)
  {
    UniversalPrint(value, os);
  }
};
template <typename T, size_t N>
class UniversalTersePrinter<T[N]>
{
public:
  static void Print(const T(&value)[N], ::std::ostream * os)
  {
    UniversalPrinter<T[N]>::Print(value, os);
  }
};
template <>
class UniversalTersePrinter<const char *>
{
public:
  static void Print(const char * str, ::std::ostream * os)
  {
    if (str == NULL)
      {
        *os << "NULL";
      }

    else
      {
        UniversalPrint(string(str), os);
      }
  }
};
template <>
class UniversalTersePrinter<char *>
{
public:
  static void Print(char * str, ::std::ostream * os)
  {
    UniversalTersePrinter<const char *>::Print(str, os);
  }
};

#if GTEST_HAS_STD_WSTRING
template <>
class UniversalTersePrinter<const wchar_t *>
{
public:
  static void Print(const wchar_t * str, ::std::ostream * os)
  {
    if (str == NULL)
      {
        *os << "NULL";
      }

    else
      {
        UniversalPrint(::std::wstring(str), os);
      }
  }
};
#endif

template <>
class UniversalTersePrinter<wchar_t *>
{
public:
  static void Print(wchar_t * str, ::std::ostream * os)
  {
    UniversalTersePrinter<const wchar_t *>::Print(str, os);
  }
};

template <typename T>
void UniversalTersePrint(const T & value, ::std::ostream * os)
{
  UniversalTersePrinter<T>::Print(value, os);
}

// Prints a value using the type inferred by the compiler.  The
// difference between this and UniversalTersePrint() is that for a
// (const) char pointer, this prints both the pointer and the
// NUL-terminated string.
template <typename T>
void UniversalPrint(const T & value, ::std::ostream * os)
{
  // A workarond for the bug in VC++ 7.1 that prevents us from instantiating
  // UniversalPrinter with T directly.
  typedef T T1;
  UniversalPrinter<T1>::Print(value, os);
}

#if GTEST_HAS_TR1_TUPLE
typedef ::std::vector<string> Strings;

// This helper template allows PrintTo() for tuples and
// UniversalTersePrintTupleFieldsToStrings() to be defined by
// induction on the number of tuple fields.  The idea is that
// TuplePrefixPrinter<N>::PrintPrefixTo(t, os) prints the first N
// fields in tuple t, and can be defined in terms of
// TuplePrefixPrinter<N - 1>.

// The inductive case.
template <size_t N>
struct TuplePrefixPrinter
{
  // Prints the first N fields of a tuple.
  template <typename Tuple>
  static void PrintPrefixTo(const Tuple & t, ::std::ostream * os)
  {
    TuplePrefixPrinter < N - 1 >::PrintPrefixTo(t, os);
    *os << ", ";
    UniversalPrinter < typename ::std::tr1::tuple_element < N - 1, Tuple >::type >
    ::Print(::std::tr1::get < N - 1 > (t), os);
  }

  // Tersely prints the first N fields of a tuple to a string vector,
  // one element for each field.
  template <typename Tuple>
  static void TersePrintPrefixToStrings(const Tuple & t, Strings * strings)
  {
    TuplePrefixPrinter < N - 1 >::TersePrintPrefixToStrings(t, strings);
    ::std::stringstream ss;
    UniversalTersePrint(::std::tr1::get < N - 1 > (t), &ss);
    strings->push_back(ss.str());
  }
};

// Base cases.
template <>
struct TuplePrefixPrinter<0>
{
  template <typename Tuple>
  static void PrintPrefixTo(const Tuple &, ::std::ostream *) {}

  template <typename Tuple>
  static void TersePrintPrefixToStrings(const Tuple &, Strings *) {}
};
// We have to specialize the entire TuplePrefixPrinter<> class
// template here, even though the definition of
// TersePrintPrefixToStrings() is the same as the generic version, as
// Embarcadero (formerly CodeGear, formerly Borland) C++ doesn't
// support specializing a method template of a class template.
template <>
struct TuplePrefixPrinter<1>
{
  template <typename Tuple>
  static void PrintPrefixTo(const Tuple & t, ::std::ostream * os)
  {
    UniversalPrinter<typename ::std::tr1::tuple_element<0, Tuple>::type>::
    Print(::std::tr1::get<0>(t), os);
  }

  template <typename Tuple>
  static void TersePrintPrefixToStrings(const Tuple & t, Strings * strings)
  {
    ::std::stringstream ss;
    UniversalTersePrint(::std::tr1::get<0>(t), &ss);
    strings->push_back(ss.str());
  }
};

// Helper function for printing a tuple.  T must be instantiated with
// a tuple type.
template <typename T>
void PrintTupleTo(const T & t, ::std::ostream * os)
{
  *os << "(";
  TuplePrefixPrinter< ::std::tr1::tuple_size<T>::value>::
  PrintPrefixTo(t, os);
  *os << ")";
}

// Prints the fields of a tuple tersely to a string vector, one
// element for each field.  See the comment before
// UniversalTersePrint() for how we define "tersely".
template <typename Tuple>
Strings UniversalTersePrintTupleFieldsToStrings(const Tuple & value)
{
  Strings result;
  TuplePrefixPrinter< ::std::tr1::tuple_size<Tuple>::value>::
  TersePrintPrefixToStrings(value, &result);
  return result;
}
#endif  // GTEST_HAS_TR1_TUPLE

}  // namespace internal

template <typename T>
::std::string PrintToString(const T & value)
{
  ::std::stringstream ss;
  internal::UniversalTersePrinter<T>::Print(value, &ss);
  return ss.str();
}

}  // namespace testing

#endif  // GTEST_INCLUDE_GTEST_GTEST_PRINTERS_H_