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// Input streams -*- C++ -*-
// Copyright (C) 1997-2016 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
//
// ISO C++ 14882: 27.6.1 Input streams
//
/** @file include/istream
* This is a Standard C++ Library header.
*/
#ifndef _GLIBCXX_ISTREAM
#define _GLIBCXX_ISTREAM 1
#pragma GCC system_header
#include <ios>
#include <ostream>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @brief Template class basic_istream.
* @ingroup io
*
* @tparam _CharT Type of character stream.
* @tparam _Traits Traits for character type, defaults to
* char_traits<_CharT>.
*
* This is the base class for all input streams. It provides text
* formatting of all builtin types, and communicates with any class
* derived from basic_streambuf to do the actual input.
*/
template<typename _CharT, typename _Traits>
class basic_istream : virtual public basic_ios<_CharT, _Traits>
{
public:
// Types (inherited from basic_ios (27.4.4)):
typedef _CharT char_type;
typedef typename _Traits::int_type int_type;
typedef typename _Traits::pos_type pos_type;
typedef typename _Traits::off_type off_type;
typedef _Traits traits_type;
// Non-standard Types:
typedef basic_streambuf<_CharT, _Traits> __streambuf_type;
typedef basic_ios<_CharT, _Traits> __ios_type;
typedef basic_istream<_CharT, _Traits> __istream_type;
typedef num_get<_CharT, istreambuf_iterator<_CharT, _Traits> >
__num_get_type;
typedef ctype<_CharT> __ctype_type;
protected:
// Data Members:
/**
* The number of characters extracted in the previous unformatted
* function; see gcount().
*/
streamsize _M_gcount;
public:
/**
* @brief Base constructor.
*
* This ctor is almost never called by the user directly, rather from
* derived classes' initialization lists, which pass a pointer to
* their own stream buffer.
*/
explicit
basic_istream(__streambuf_type* __sb)
: _M_gcount(streamsize(0))
{ this->init(__sb); }
/**
* @brief Base destructor.
*
* This does very little apart from providing a virtual base dtor.
*/
virtual
~basic_istream()
{ _M_gcount = streamsize(0); }
/// Safe prefix/suffix operations.
class sentry;
friend class sentry;
//@{
/**
* @brief Interface for manipulators.
*
* Manipulators such as @c std::ws and @c std::dec use these
* functions in constructs like
* <code>std::cin >> std::ws</code>.
* For more information, see the iomanip header.
*/
__istream_type&
operator>>(__istream_type& (*__pf)(__istream_type&))
{ return __pf(*this); }
__istream_type&
operator>>(__ios_type& (*__pf)(__ios_type&))
{
__pf(*this);
return *this;
}
__istream_type&
operator>>(ios_base& (*__pf)(ios_base&))
{
__pf(*this);
return *this;
}
//@}
//@{
/**
* @name Extractors
*
* All the @c operator>> functions (aka <em>formatted input
* functions</em>) have some common behavior. Each starts by
* constructing a temporary object of type std::basic_istream::sentry
* with the second argument (noskipws) set to false. This has several
* effects, concluding with the setting of a status flag; see the
* sentry documentation for more.
*
* If the sentry status is good, the function tries to extract
* whatever data is appropriate for the type of the argument.
*
* If an exception is thrown during extraction, ios_base::badbit
* will be turned on in the stream's error state without causing an
* ios_base::failure to be thrown. The original exception will then
* be rethrown.
*/
//@{
/**
* @brief Integer arithmetic extractors
* @param __n A variable of builtin integral type.
* @return @c *this if successful
*
* These functions use the stream's current locale (specifically, the
* @c num_get facet) to parse the input data.
*/
__istream_type&
operator>>(bool& __n)
{ return _M_extract(__n); }
__istream_type&
operator>>(short& __n);
__istream_type&
operator>>(unsigned short& __n)
{ return _M_extract(__n); }
__istream_type&
operator>>(int& __n);
__istream_type&
operator>>(unsigned int& __n)
{ return _M_extract(__n); }
__istream_type&
operator>>(long& __n)
{ return _M_extract(__n); }
__istream_type&
operator>>(unsigned long& __n)
{ return _M_extract(__n); }
#ifdef _GLIBCXX_USE_LONG_LONG
__istream_type&
operator>>(long long& __n)
{ return _M_extract(__n); }
__istream_type&
operator>>(unsigned long long& __n)
{ return _M_extract(__n); }
#endif
//@}
//@{
/**
* @brief Floating point arithmetic extractors
* @param __f A variable of builtin floating point type.
* @return @c *this if successful
*
* These functions use the stream's current locale (specifically, the
* @c num_get facet) to parse the input data.
*/
__istream_type&
operator>>(float& __f)
{ return _M_extract(__f); }
__istream_type&
operator>>(double& __f)
{ return _M_extract(__f); }
__istream_type&
operator>>(long double& __f)
{ return _M_extract(__f); }
//@}
/**
* @brief Basic arithmetic extractors
* @param __p A variable of pointer type.
* @return @c *this if successful
*
* These functions use the stream's current locale (specifically, the
* @c num_get facet) to parse the input data.
*/
__istream_type&
operator>>(void*& __p)
{ return _M_extract(__p); }
/**
* @brief Extracting into another streambuf.
* @param __sb A pointer to a streambuf
*
* This function behaves like one of the basic arithmetic extractors,
* in that it also constructs a sentry object and has the same error
* handling behavior.
*
* If @p __sb is NULL, the stream will set failbit in its error state.
*
* Characters are extracted from this stream and inserted into the
* @p __sb streambuf until one of the following occurs:
*
* - the input stream reaches end-of-file,
* - insertion into the output buffer fails (in this case, the
* character that would have been inserted is not extracted), or
* - an exception occurs (and in this case is caught)
*
* If the function inserts no characters, failbit is set.
*/
__istream_type&
operator>>(__streambuf_type* __sb);
//@}
// [27.6.1.3] unformatted input
/**
* @brief Character counting
* @return The number of characters extracted by the previous
* unformatted input function dispatched for this stream.
*/
streamsize
gcount() const
{ return _M_gcount; }
//@{
/**
* @name Unformatted Input Functions
*
* All the unformatted input functions have some common behavior.
* Each starts by constructing a temporary object of type
* std::basic_istream::sentry with the second argument (noskipws)
* set to true. This has several effects, concluding with the
* setting of a status flag; see the sentry documentation for more.
*
* If the sentry status is good, the function tries to extract
* whatever data is appropriate for the type of the argument.
*
* The number of characters extracted is stored for later retrieval
* by gcount().
*
* If an exception is thrown during extraction, ios_base::badbit
* will be turned on in the stream's error state without causing an
* ios_base::failure to be thrown. The original exception will then
* be rethrown.
*/
/**
* @brief Simple extraction.
* @return A character, or eof().
*
* Tries to extract a character. If none are available, sets failbit
* and returns traits::eof().
*/
int_type
get();
/**
* @brief Simple extraction.
* @param __c The character in which to store data.
* @return *this
*
* Tries to extract a character and store it in @a __c. If none are
* available, sets failbit and returns traits::eof().
*
* @note This function is not overloaded on signed char and
* unsigned char.
*/
__istream_type&
get(char_type& __c);
/**
* @brief Simple multiple-character extraction.
* @param __s Pointer to an array.
* @param __n Maximum number of characters to store in @a __s.
* @param __delim A "stop" character.
* @return *this
*
* Characters are extracted and stored into @a __s until one of the
* following happens:
*
* - @c __n-1 characters are stored
* - the input sequence reaches EOF
* - the next character equals @a __delim, in which case the character
* is not extracted
*
* If no characters are stored, failbit is set in the stream's error
* state.
*
* In any case, a null character is stored into the next location in
* the array.
*
* @note This function is not overloaded on signed char and
* unsigned char.
*/
__istream_type&
get(char_type* __s, streamsize __n, char_type __delim);
/**
* @brief Simple multiple-character extraction.
* @param __s Pointer to an array.
* @param __n Maximum number of characters to store in @a s.
* @return *this
*
* Returns @c get(__s,__n,widen(&apos;\\n&apos;)).
*/
__istream_type&
get(char_type* __s, streamsize __n)
{ return this->get(__s, __n, this->widen('\n')); }
/**
* @brief Extraction into another streambuf.
* @param __sb A streambuf in which to store data.
* @param __delim A "stop" character.
* @return *this
*
* Characters are extracted and inserted into @a __sb until one of the
* following happens:
*
* - the input sequence reaches EOF
* - insertion into the output buffer fails (in this case, the
* character that would have been inserted is not extracted)
* - the next character equals @a __delim (in this case, the character
* is not extracted)
* - an exception occurs (and in this case is caught)
*
* If no characters are stored, failbit is set in the stream's error
* state.
*/
__istream_type&
get(__streambuf_type& __sb, char_type __delim);
/**
* @brief Extraction into another streambuf.
* @param __sb A streambuf in which to store data.
* @return *this
*
* Returns @c get(__sb,widen(&apos;\\n&apos;)).
*/
__istream_type&
get(__streambuf_type& __sb)
{ return this->get(__sb, this->widen('\n')); }
/**
* @brief String extraction.
* @param __s A character array in which to store the data.
* @param __n Maximum number of characters to extract.
* @param __delim A "stop" character.
* @return *this
*
* Extracts and stores characters into @a __s until one of the
* following happens. Note that these criteria are required to be
* tested in the order listed here, to allow an input line to exactly
* fill the @a __s array without setting failbit.
*
* -# the input sequence reaches end-of-file, in which case eofbit
* is set in the stream error state
* -# the next character equals @c __delim, in which case the character
* is extracted (and therefore counted in @c gcount()) but not stored
* -# @c __n-1 characters are stored, in which case failbit is set
* in the stream error state
*
* If no characters are extracted, failbit is set. (An empty line of
* input should therefore not cause failbit to be set.)
*
* In any case, a null character is stored in the next location in
* the array.
*/
__istream_type&
getline(char_type* __s, streamsize __n, char_type __delim);
/**
* @brief String extraction.
* @param __s A character array in which to store the data.
* @param __n Maximum number of characters to extract.
* @return *this
*
* Returns @c getline(__s,__n,widen(&apos;\\n&apos;)).
*/
__istream_type&
getline(char_type* __s, streamsize __n)
{ return this->getline(__s, __n, this->widen('\n')); }
/**
* @brief Discarding characters
* @param __n Number of characters to discard.
* @param __delim A "stop" character.
* @return *this
*
* Extracts characters and throws them away until one of the
* following happens:
* - if @a __n @c != @c std::numeric_limits<int>::max(), @a __n
* characters are extracted
* - the input sequence reaches end-of-file
* - the next character equals @a __delim (in this case, the character
* is extracted); note that this condition will never occur if
* @a __delim equals @c traits::eof().
*
* NB: Provide three overloads, instead of the single function
* (with defaults) mandated by the Standard: this leads to a
* better performing implementation, while still conforming to
* the Standard.
*/
__istream_type&
ignore(streamsize __n, int_type __delim);
__istream_type&
ignore(streamsize __n);
__istream_type&
ignore();
/**
* @brief Looking ahead in the stream
* @return The next character, or eof().
*
* If, after constructing the sentry object, @c good() is false,
* returns @c traits::eof(). Otherwise reads but does not extract
* the next input character.
*/
int_type
peek();
/**
* @brief Extraction without delimiters.
* @param __s A character array.
* @param __n Maximum number of characters to store.
* @return *this
*
* If the stream state is @c good(), extracts characters and stores
* them into @a __s until one of the following happens:
* - @a __n characters are stored
* - the input sequence reaches end-of-file, in which case the error
* state is set to @c failbit|eofbit.
*
* @note This function is not overloaded on signed char and
* unsigned char.
*/
__istream_type&
read(char_type* __s, streamsize __n);
/**
* @brief Extraction until the buffer is exhausted, but no more.
* @param __s A character array.
* @param __n Maximum number of characters to store.
* @return The number of characters extracted.
*
* Extracts characters and stores them into @a __s depending on the
* number of characters remaining in the streambuf's buffer,
* @c rdbuf()->in_avail(), called @c A here:
* - if @c A @c == @c -1, sets eofbit and extracts no characters
* - if @c A @c == @c 0, extracts no characters
* - if @c A @c > @c 0, extracts @c min(A,n)
*
* The goal is to empty the current buffer, and to not request any
* more from the external input sequence controlled by the streambuf.
*/
streamsize
readsome(char_type* __s, streamsize __n);
/**
* @brief Unextracting a single character.
* @param __c The character to push back into the input stream.
* @return *this
*
* If @c rdbuf() is not null, calls @c rdbuf()->sputbackc(c).
*
* If @c rdbuf() is null or if @c sputbackc() fails, sets badbit in
* the error state.
*
* @note This function first clears eofbit. Since no characters
* are extracted, the next call to @c gcount() will return 0,
* as required by DR 60.
*/
__istream_type&
putback(char_type __c);
/**
* @brief Unextracting the previous character.
* @return *this
*
* If @c rdbuf() is not null, calls @c rdbuf()->sungetc(c).
*
* If @c rdbuf() is null or if @c sungetc() fails, sets badbit in
* the error state.
*
* @note This function first clears eofbit. Since no characters
* are extracted, the next call to @c gcount() will return 0,
* as required by DR 60.
*/
__istream_type&
unget();
/**
* @brief Synchronizing the stream buffer.
* @return 0 on success, -1 on failure
*
* If @c rdbuf() is a null pointer, returns -1.
*
* Otherwise, calls @c rdbuf()->pubsync(), and if that returns -1,
* sets badbit and returns -1.
*
* Otherwise, returns 0.
*
* @note This function does not count the number of characters
* extracted, if any, and therefore does not affect the next
* call to @c gcount().
*/
int
sync();
/**
* @brief Getting the current read position.
* @return A file position object.
*
* If @c fail() is not false, returns @c pos_type(-1) to indicate
* failure. Otherwise returns @c rdbuf()->pubseekoff(0,cur,in).
*
* @note This function does not count the number of characters
* extracted, if any, and therefore does not affect the next
* call to @c gcount(). At variance with putback, unget and
* seekg, eofbit is not cleared first.
*/
pos_type
tellg();
/**
* @brief Changing the current read position.
* @param __pos A file position object.
* @return *this
*
* If @c fail() is not true, calls @c rdbuf()->pubseekpos(__pos). If
* that function fails, sets failbit.
*
* @note This function first clears eofbit. It does not count the
* number of characters extracted, if any, and therefore does
* not affect the next call to @c gcount().
*/
__istream_type&
seekg(pos_type);
/**
* @brief Changing the current read position.
* @param __off A file offset object.
* @param __dir The direction in which to seek.
* @return *this
*
* If @c fail() is not true, calls @c rdbuf()->pubseekoff(__off,__dir).
* If that function fails, sets failbit.
*
* @note This function first clears eofbit. It does not count the
* number of characters extracted, if any, and therefore does
* not affect the next call to @c gcount().
*/
__istream_type&
seekg(off_type, ios_base::seekdir);
//@}
protected:
basic_istream()
: _M_gcount(streamsize(0))
{ this->init(0); }
#if __cplusplus >= 201103L
basic_istream(const basic_istream&) = delete;
basic_istream(basic_istream&& __rhs)
: __ios_type(), _M_gcount(__rhs._M_gcount)
{
__ios_type::move(__rhs);
__rhs._M_gcount = 0;
}
// 27.7.3.3 Assign/swap
basic_istream& operator=(const basic_istream&) = delete;
basic_istream&
operator=(basic_istream&& __rhs)
{
swap(__rhs);
return *this;
}
void
swap(basic_istream& __rhs)
{
__ios_type::swap(__rhs);
std::swap(_M_gcount, __rhs._M_gcount);
}
#endif
template<typename _ValueT>
__istream_type&
_M_extract(_ValueT& __v);
};
/// Explicit specialization declarations, defined in src/istream.cc.
template<>
basic_istream<char>&
basic_istream<char>::
getline(char_type* __s, streamsize __n, char_type __delim);
template<>
basic_istream<char>&
basic_istream<char>::
ignore(streamsize __n);
template<>
basic_istream<char>&
basic_istream<char>::
ignore(streamsize __n, int_type __delim);
#ifdef _GLIBCXX_USE_WCHAR_T
template<>
basic_istream<wchar_t>&
basic_istream<wchar_t>::
getline(char_type* __s, streamsize __n, char_type __delim);
template<>
basic_istream<wchar_t>&
basic_istream<wchar_t>::
ignore(streamsize __n);
template<>
basic_istream<wchar_t>&
basic_istream<wchar_t>::
ignore(streamsize __n, int_type __delim);
#endif
/**
* @brief Performs setup work for input streams.
*
* Objects of this class are created before all of the standard
* extractors are run. It is responsible for <em>exception-safe
* prefix and suffix operations,</em> although only prefix actions
* are currently required by the standard.
*/
template<typename _CharT, typename _Traits>
class basic_istream<_CharT, _Traits>::sentry
{
// Data Members.
bool _M_ok;
public:
/// Easy access to dependent types.
typedef _Traits traits_type;
typedef basic_streambuf<_CharT, _Traits> __streambuf_type;
typedef basic_istream<_CharT, _Traits> __istream_type;
typedef typename __istream_type::__ctype_type __ctype_type;
typedef typename _Traits::int_type __int_type;
/**
* @brief The constructor performs all the work.
* @param __is The input stream to guard.
* @param __noskipws Whether to consume whitespace or not.
*
* If the stream state is good (@a __is.good() is true), then the
* following actions are performed, otherwise the sentry state
* is false (<em>not okay</em>) and failbit is set in the
* stream state.
*
* The sentry's preparatory actions are:
*
* -# if the stream is tied to an output stream, @c is.tie()->flush()
* is called to synchronize the output sequence
* -# if @a __noskipws is false, and @c ios_base::skipws is set in
* @c is.flags(), the sentry extracts and discards whitespace
* characters from the stream. The currently imbued locale is
* used to determine whether each character is whitespace.
*
* If the stream state is still good, then the sentry state becomes
* true (@a okay).
*/
explicit
sentry(basic_istream<_CharT, _Traits>& __is, bool __noskipws = false);
/**
* @brief Quick status checking.
* @return The sentry state.
*
* For ease of use, sentries may be converted to booleans. The
* return value is that of the sentry state (true == okay).
*/
#if __cplusplus >= 201103L
explicit
#endif
operator bool() const
{ return _M_ok; }
};
//@{
/**
* @brief Character extractors
* @param __in An input stream.
* @param __c A character reference.
* @return in
*
* Behaves like one of the formatted arithmetic extractors described in
* std::basic_istream. After constructing a sentry object with good
* status, this function extracts a character (if one is available) and
* stores it in @a __c. Otherwise, sets failbit in the input stream.
*/
template<typename _CharT, typename _Traits>
basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c);
template<class _Traits>
inline basic_istream<char, _Traits>&
operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
{ return (__in >> reinterpret_cast<char&>(__c)); }
template<class _Traits>
inline basic_istream<char, _Traits>&
operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
{ return (__in >> reinterpret_cast<char&>(__c)); }
//@}
//@{
/**
* @brief Character string extractors
* @param __in An input stream.
* @param __s A pointer to a character array.
* @return __in
*
* Behaves like one of the formatted arithmetic extractors described in
* std::basic_istream. After constructing a sentry object with good
* status, this function extracts up to @c n characters and stores them
* into the array starting at @a __s. @c n is defined as:
*
* - if @c width() is greater than zero, @c n is width() otherwise
* - @c n is <em>the number of elements of the largest array of *
* - @c char_type that can store a terminating @c eos.</em>
* - [27.6.1.2.3]/6
*
* Characters are extracted and stored until one of the following happens:
* - @c n-1 characters are stored
* - EOF is reached
* - the next character is whitespace according to the current locale
* - the next character is a null byte (i.e., @c charT() )
*
* @c width(0) is then called for the input stream.
*
* If no characters are extracted, sets failbit.
*/
template<typename _CharT, typename _Traits>
basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s);
// Explicit specialization declaration, defined in src/istream.cc.
template<>
basic_istream<char>&
operator>>(basic_istream<char>& __in, char* __s);
template<class _Traits>
inline basic_istream<char, _Traits>&
operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
{ return (__in >> reinterpret_cast<char*>(__s)); }
template<class _Traits>
inline basic_istream<char, _Traits>&
operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
{ return (__in >> reinterpret_cast<char*>(__s)); }
//@}
/**
* @brief Template class basic_iostream
* @ingroup io
*
* @tparam _CharT Type of character stream.
* @tparam _Traits Traits for character type, defaults to
* char_traits<_CharT>.
*
* This class multiply inherits from the input and output stream classes
* simply to provide a single interface.
*/
template<typename _CharT, typename _Traits>
class basic_iostream
: public basic_istream<_CharT, _Traits>,
public basic_ostream<_CharT, _Traits>
{
public:
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 271. basic_iostream missing typedefs
// Types (inherited):
typedef _CharT char_type;
typedef typename _Traits::int_type int_type;
typedef typename _Traits::pos_type pos_type;
typedef typename _Traits::off_type off_type;
typedef _Traits traits_type;
// Non-standard Types:
typedef basic_istream<_CharT, _Traits> __istream_type;
typedef basic_ostream<_CharT, _Traits> __ostream_type;
/**
* @brief Constructor does nothing.
*
* Both of the parent classes are initialized with the same
* streambuf pointer passed to this constructor.
*/
explicit
basic_iostream(basic_streambuf<_CharT, _Traits>* __sb)
: __istream_type(__sb), __ostream_type(__sb) { }
/**
* @brief Destructor does nothing.
*/
virtual
~basic_iostream() { }
protected:
basic_iostream()
: __istream_type(), __ostream_type() { }
#if __cplusplus >= 201103L
basic_iostream(const basic_iostream&) = delete;
basic_iostream(basic_iostream&& __rhs)
: __istream_type(std::move(__rhs)), __ostream_type(*this)
{ }
// 27.7.3.3 Assign/swap
basic_iostream& operator=(const basic_iostream&) = delete;
basic_iostream&
operator=(basic_iostream&& __rhs)
{
swap(__rhs);
return *this;
}
void
swap(basic_iostream& __rhs)
{ __istream_type::swap(__rhs); }
#endif
};
/**
* @brief Quick and easy way to eat whitespace
*
* This manipulator extracts whitespace characters, stopping when the
* next character is non-whitespace, or when the input sequence is empty.
* If the sequence is empty, @c eofbit is set in the stream, but not
* @c failbit.
*
* The current locale is used to distinguish whitespace characters.
*
* Example:
* @code
* MyClass mc;
*
* std::cin >> std::ws >> mc;
* @endcode
* will skip leading whitespace before calling operator>> on cin and your
* object. Note that the same effect can be achieved by creating a
* std::basic_istream::sentry inside your definition of operator>>.
*/
template<typename _CharT, typename _Traits>
basic_istream<_CharT, _Traits>&
ws(basic_istream<_CharT, _Traits>& __is);
#if __cplusplus >= 201103L
// [27.7.1.6] Rvalue stream extraction
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2328. Rvalue stream extraction should use perfect forwarding
/**
* @brief Generic extractor for rvalue stream
* @param __is An input stream.
* @param __x A reference to the extraction target.
* @return is
*
* This is just a forwarding function to allow extraction from
* rvalue streams since they won't bind to the extractor functions
* that take an lvalue reference.
*/
template<typename _CharT, typename _Traits, typename _Tp>
inline basic_istream<_CharT, _Traits>&
operator>>(basic_istream<_CharT, _Traits>&& __is, _Tp&& __x)
{
__is >> std::forward<_Tp>(__x);
return __is;
}
#endif // C++11
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#include <bits/istream.tcc>
#endif /* _GLIBCXX_ISTREAM */
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