istream

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      /**
       *  @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('\n')).
      */
      inline __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().
      */
      __istream_type& 
      ignore(streamsize __n = 1, int_type __delim = traits_type::eof());
      
      /**
       *  @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  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  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().
      */
      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 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 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:
      explicit 
      basic_istream(): _M_gcount(streamsize(0)) { }
    };
  
  /**
   *  @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 "exception-safe prefix and
   *  suffix operations," although only prefix actions are currently required
   *  by the standard.  Additional actions may be added by the
   *  implementation, and we list them in
   *  http://gcc.gnu.org/onlinedocs/libstdc++/17_intro/howto.html#5
   *  under [27.6] notes.
  */
  template<typename _CharT, typename _Traits>
    class basic_istream<_CharT, _Traits>::sentry
    {
    public:
      /// Easy access to dependant 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 ("not okay") 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 ("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).
      */
      operator bool() const { return _M_ok; }

    private:
      bool _M_ok;
    };

  // [27.6.1.2.3] character extraction templates
  //@{
  /**
   *  @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>
    basic_istream<char, _Traits>&
    operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
    { return (__in >> reinterpret_cast<char&>(__c)); }

  template<class _Traits>
    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 "the number of elements of the largest array of
   *    @c char_type that can store a terminating @c eos." [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);
  
  template<class _Traits>
    basic_istream<char,_Traits>&
    operator>>(basic_istream<char,_Traits>& __in, unsigned char* __s)
    { return (__in >> reinterpret_cast<char*>(__s)); }

  template<class _Traits>
    basic_istream<char,_Traits>&
    operator>>(basic_istream<char,_Traits>& __in, signed char* __s)
    { return (__in >> reinterpret_cast<char*>(__s)); }
  //@}

  // 27.6.1.5 Template class basic_iostream
  /**
   *  @brief  Merging istream and ostream capabilities.
   *
   *  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(), __ostream_type()
      { this->init(__sb); }

      /**
       *  @brief  Destructor does nothing.
      */
      virtual 
      ~basic_iostream() { }

    protected:
      explicit 
      basic_iostream() : __istream_type(), __ostream_type()
      { }
    };

  // [27.6.1.4] standard basic_istream manipulators
  /**
   *  @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);
} // namespace std

#ifndef _GLIBCXX_EXPORT_TEMPLATE
# include <bits/istream.tcc>
#endif

#endif	/* _GLIBCXX_ISTREAM */