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/usr/include/c++/11/istream


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     1	// Input streams -*- C++ -*-
     2	
     3	// Copyright (C) 1997-2021 Free Software Foundation, Inc.
     4	//
     5	// This file is part of the GNU ISO C++ Library.  This library is free
     6	// software; you can redistribute it and/or modify it under the
     7	// terms of the GNU General Public License as published by the
     8	// Free Software Foundation; either version 3, or (at your option)
     9	// any later version.
    10	
    11	// This library is distributed in the hope that it will be useful,
    12	// but WITHOUT ANY WARRANTY; without even the implied warranty of
    13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    14	// GNU General Public License for more details.
    15	
    16	// Under Section 7 of GPL version 3, you are granted additional
    17	// permissions described in the GCC Runtime Library Exception, version
    18	// 3.1, as published by the Free Software Foundation.
    19	
    20	// You should have received a copy of the GNU General Public License and
    21	// a copy of the GCC Runtime Library Exception along with this program;
    22	// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    23	// <http://www.gnu.org/licenses/>.
    24	
    25	//
    26	// ISO C++ 14882: 27.6.1  Input streams
    27	//
    28	
    29	/** @file include/istream
    30	 *  This is a Standard C++ Library header.
    31	 */
    32	
    33	#ifndef _GLIBCXX_ISTREAM
    34	#define _GLIBCXX_ISTREAM 1
    35	
    36	#pragma GCC system_header
    37	
    38	#include <ios>
    39	#include <ostream>
    40	
    41	namespace std _GLIBCXX_VISIBILITY(default)
    42	{
    43	_GLIBCXX_BEGIN_NAMESPACE_VERSION
    44	
    45	  /**
    46	   *  @brief  Template class basic_istream.
    47	   *  @ingroup io
    48	   *
    49	   *  @tparam _CharT  Type of character stream.
    50	   *  @tparam _Traits  Traits for character type, defaults to
    51	   *                   char_traits<_CharT>.
    52	   *
    53	   *  This is the base class for all input streams.  It provides text
    54	   *  formatting of all builtin types, and communicates with any class
    55	   *  derived from basic_streambuf to do the actual input.
    56	  */
    57	  template<typename _CharT, typename _Traits>
    58	    class basic_istream : virtual public basic_ios<_CharT, _Traits>
    59	    {
    60	    public:
    61	      // Types (inherited from basic_ios (27.4.4)):
    62	      typedef _CharT			 		char_type;
    63	      typedef typename _Traits::int_type 		int_type;
    64	      typedef typename _Traits::pos_type 		pos_type;
    65	      typedef typename _Traits::off_type 		off_type;
    66	      typedef _Traits			 		traits_type;
    67	
    68	      // Non-standard Types:
    69	      typedef basic_streambuf<_CharT, _Traits> 		__streambuf_type;
    70	      typedef basic_ios<_CharT, _Traits>		__ios_type;
    71	      typedef basic_istream<_CharT, _Traits>		__istream_type;
    72	      typedef num_get<_CharT, istreambuf_iterator<_CharT, _Traits> >
    73	 							__num_get_type;
    74	      typedef ctype<_CharT>	      			__ctype_type;
    75	
    76	    protected:
    77	      // Data Members:
    78	      /**
    79	       *  The number of characters extracted in the previous unformatted
    80	       *  function; see gcount().
    81	      */
    82	      streamsize 		_M_gcount;
    83	
    84	    public:
    85	      /**
    86	       *  @brief  Base constructor.
    87	       *
    88	       *  This ctor is almost never called by the user directly, rather from
    89	       *  derived classes' initialization lists, which pass a pointer to
    90	       *  their own stream buffer.
    91	      */
    92	      explicit
    93	      basic_istream(__streambuf_type* __sb)
    94	      : _M_gcount(streamsize(0))
    95	      { this->init(__sb); }
    96	
    97	      /**
    98	       *  @brief  Base destructor.
    99	       *
   100	       *  This does very little apart from providing a virtual base dtor.
   101	      */
   102	      virtual
   103	      ~basic_istream()
   104	      { _M_gcount = streamsize(0); }
   105	
   106	      /// Safe prefix/suffix operations.
   107	      class sentry;
   108	      friend class sentry;
   109	
   110	      ///@{
   111	      /**
   112	       *  @brief  Interface for manipulators.
   113	       *
   114	       *  Manipulators such as @c std::ws and @c std::dec use these
   115	       *  functions in constructs like
   116	       *  <code>std::cin >> std::ws</code>.
   117	       *  For more information, see the iomanip header.
   118	      */
   119	      __istream_type&
   120	      operator>>(__istream_type& (*__pf)(__istream_type&))
   121	      { return __pf(*this); }
   122	
   123	      __istream_type&
   124	      operator>>(__ios_type& (*__pf)(__ios_type&))
   125	      {
   126		__pf(*this);
   127		return *this;
   128	      }
   129	
   130	      __istream_type&
   131	      operator>>(ios_base& (*__pf)(ios_base&))
   132	      {
   133		__pf(*this);
   134		return *this;
   135	      }
   136	      ///@}
   137	
   138	      ///@{
   139	      /**
   140	       *  @name Extractors
   141	       *
   142	       *  All the @c operator>> functions (aka <em>formatted input
   143	       *  functions</em>) have some common behavior.  Each starts by
   144	       *  constructing a temporary object of type std::basic_istream::sentry
   145	       *  with the second argument (noskipws) set to false.  This has several
   146	       *  effects, concluding with the setting of a status flag; see the
   147	       *  sentry documentation for more.
   148	       *
   149	       *  If the sentry status is good, the function tries to extract
   150	       *  whatever data is appropriate for the type of the argument.
   151	       *
   152	       *  If an exception is thrown during extraction, ios_base::badbit
   153	       *  will be turned on in the stream's error state (without causing an
   154	       *  ios_base::failure to be thrown) and the original exception will
   155	       *  be rethrown if badbit is set in the exceptions mask.
   156	      */
   157	
   158	      ///@{
   159	      /**
   160	       *  @brief  Integer arithmetic extractors
   161	       *  @param  __n A variable of builtin integral type.
   162	       *  @return  @c *this if successful
   163	       *
   164	       *  These functions use the stream's current locale (specifically, the
   165	       *  @c num_get facet) to parse the input data.
   166	      */
   167	      __istream_type&
   168	      operator>>(bool& __n)
   169	      { return _M_extract(__n); }
   170	
   171	      __istream_type&
   172	      operator>>(short& __n);
   173	
   174	      __istream_type&
   175	      operator>>(unsigned short& __n)
   176	      { return _M_extract(__n); }
   177	
   178	      __istream_type&
   179	      operator>>(int& __n);
   180	
   181	      __istream_type&
   182	      operator>>(unsigned int& __n)
   183	      { return _M_extract(__n); }
   184	
   185	      __istream_type&
   186	      operator>>(long& __n)
   187	      { return _M_extract(__n); }
   188	
   189	      __istream_type&
   190	      operator>>(unsigned long& __n)
   191	      { return _M_extract(__n); }
   192	
   193	#ifdef _GLIBCXX_USE_LONG_LONG
   194	      __istream_type&
   195	      operator>>(long long& __n)
   196	      { return _M_extract(__n); }
   197	
   198	      __istream_type&
   199	      operator>>(unsigned long long& __n)
   200	      { return _M_extract(__n); }
   201	#endif
   202	      ///@}
   203	
   204	      ///@{
   205	      /**
   206	       *  @brief  Floating point arithmetic extractors
   207	       *  @param  __f A variable of builtin floating point type.
   208	       *  @return  @c *this if successful
   209	       *
   210	       *  These functions use the stream's current locale (specifically, the
   211	       *  @c num_get facet) to parse the input data.
   212	      */
   213	      __istream_type&
   214	      operator>>(float& __f)
   215	      { return _M_extract(__f); }
   216	
   217	      __istream_type&
   218	      operator>>(double& __f)
   219	      { return _M_extract(__f); }
   220	
   221	      __istream_type&
   222	      operator>>(long double& __f)
   223	      { return _M_extract(__f); }
   224	      ///@}
   225	
   226	      /**
   227	       *  @brief  Basic arithmetic extractors
   228	       *  @param  __p A variable of pointer type.
   229	       *  @return  @c *this if successful
   230	       *
   231	       *  These functions use the stream's current locale (specifically, the
   232	       *  @c num_get facet) to parse the input data.
   233	      */
   234	      __istream_type&
   235	      operator>>(void*& __p)
   236	      { return _M_extract(__p); }
   237	
   238	      /**
   239	       *  @brief  Extracting into another streambuf.
   240	       *  @param  __sb  A pointer to a streambuf
   241	       *
   242	       *  This function behaves like one of the basic arithmetic extractors,
   243	       *  in that it also constructs a sentry object and has the same error
   244	       *  handling behavior.
   245	       *
   246	       *  If @p __sb is NULL, the stream will set failbit in its error state.
   247	       *
   248	       *  Characters are extracted from this stream and inserted into the
   249	       *  @p __sb streambuf until one of the following occurs:
   250	       *
   251	       *  - the input stream reaches end-of-file,
   252	       *  - insertion into the output buffer fails (in this case, the
   253	       *    character that would have been inserted is not extracted), or
   254	       *  - an exception occurs (and in this case is caught)
   255	       *
   256	       *  If the function inserts no characters, failbit is set.
   257	      */
   258	      __istream_type&
   259	      operator>>(__streambuf_type* __sb);
   260	      ///@}
   261	
   262	      // [27.6.1.3] unformatted input
   263	      /**
   264	       *  @brief  Character counting
   265	       *  @return  The number of characters extracted by the previous
   266	       *           unformatted input function dispatched for this stream.
   267	      */
   268	      streamsize
   269	      gcount() const
   270	      { return _M_gcount; }
   271	
   272	      ///@{
   273	      /**
   274	       *  @name Unformatted Input Functions
   275	       *
   276	       *  All the unformatted input functions have some common behavior.
   277	       *  Each starts by constructing a temporary object of type
   278	       *  std::basic_istream::sentry with the second argument (noskipws)
   279	       *  set to true.  This has several effects, concluding with the
   280	       *  setting of a status flag; see the sentry documentation for more.
   281	       *
   282	       *  If the sentry status is good, the function tries to extract
   283	       *  whatever data is appropriate for the type of the argument.
   284	       *
   285	       *  The number of characters extracted is stored for later retrieval
   286	       *  by gcount().
   287	       *
   288	       *  If an exception is thrown during extraction, ios_base::badbit
   289	       *  will be turned on in the stream's error state (without causing an
   290	       *  ios_base::failure to be thrown) and the original exception will
   291	       *  be rethrown if badbit is set in the exceptions mask.
   292	      */
   293	
   294	      /**
   295	       *  @brief  Simple extraction.
   296	       *  @return  A character, or eof().
   297	       *
   298	       *  Tries to extract a character.  If none are available, sets failbit
   299	       *  and returns traits::eof().
   300	      */
   301	      int_type
   302	      get();
   303	
   304	      /**
   305	       *  @brief  Simple extraction.
   306	       *  @param  __c  The character in which to store data.
   307	       *  @return  *this
   308	       *
   309	       *  Tries to extract a character and store it in @a __c.  If none are
   310	       *  available, sets failbit and returns traits::eof().
   311	       *
   312	       *  @note  This function is not overloaded on signed char and
   313	       *         unsigned char.
   314	      */
   315	      __istream_type&
   316	      get(char_type& __c);
   317	
   318	      /**
   319	       *  @brief  Simple multiple-character extraction.
   320	       *  @param  __s  Pointer to an array.
   321	       *  @param  __n  Maximum number of characters to store in @a __s.
   322	       *  @param  __delim  A "stop" character.
   323	       *  @return  *this
   324	       *
   325	       *  Characters are extracted and stored into @a __s until one of the
   326	       *  following happens:
   327	       *
   328	       *  - @c __n-1 characters are stored
   329	       *  - the input sequence reaches EOF
   330	       *  - the next character equals @a __delim, in which case the character
   331	       *    is not extracted
   332	       *
   333	       * If no characters are stored, failbit is set in the stream's error
   334	       * state.
   335	       *
   336	       * In any case, a null character is stored into the next location in
   337	       * the array.
   338	       *
   339	       *  @note  This function is not overloaded on signed char and
   340	       *         unsigned char.
   341	      */
   342	      __istream_type&
   343	      get(char_type* __s, streamsize __n, char_type __delim);
   344	
   345	      /**
   346	       *  @brief  Simple multiple-character extraction.
   347	       *  @param  __s  Pointer to an array.
   348	       *  @param  __n  Maximum number of characters to store in @a s.
   349	       *  @return  *this
   350	       *
   351	       *  Returns @c get(__s,__n,widen('\\n')).
   352	      */
   353	      __istream_type&
   354	      get(char_type* __s, streamsize __n)
   355	      { return this->get(__s, __n, this->widen('\n')); }
   356	
   357	      /**
   358	       *  @brief  Extraction into another streambuf.
   359	       *  @param  __sb  A streambuf in which to store data.
   360	       *  @param  __delim  A "stop" character.
   361	       *  @return  *this
   362	       *
   363	       *  Characters are extracted and inserted into @a __sb until one of the
   364	       *  following happens:
   365	       *
   366	       *  - the input sequence reaches EOF
   367	       *  - insertion into the output buffer fails (in this case, the
   368	       *    character that would have been inserted is not extracted)
   369	       *  - the next character equals @a __delim (in this case, the character
   370	       *    is not extracted)
   371	       *  - an exception occurs (and in this case is caught)
   372	       *
   373	       * If no characters are stored, failbit is set in the stream's error
   374	       * state.
   375	      */
   376	      __istream_type&
   377	      get(__streambuf_type& __sb, char_type __delim);
   378	
   379	      /**
   380	       *  @brief  Extraction into another streambuf.
   381	       *  @param  __sb  A streambuf in which to store data.
   382	       *  @return  *this
   383	       *
   384	       *  Returns @c get(__sb,widen('\\n')).
   385	      */
   386	      __istream_type&
   387	      get(__streambuf_type& __sb)
   388	      { return this->get(__sb, this->widen('\n')); }
   389	
   390	      /**
   391	       *  @brief  String extraction.
   392	       *  @param  __s  A character array in which to store the data.
   393	       *  @param  __n  Maximum number of characters to extract.
   394	       *  @param  __delim  A "stop" character.
   395	       *  @return  *this
   396	       *
   397	       *  Extracts and stores characters into @a __s until one of the
   398	       *  following happens.  Note that these criteria are required to be
   399	       *  tested in the order listed here, to allow an input line to exactly
   400	       *  fill the @a __s array without setting failbit.
   401	       *
   402	       *  -# the input sequence reaches end-of-file, in which case eofbit
   403	       *     is set in the stream error state
   404	       *  -# the next character equals @c __delim, in which case the character
   405	       *     is extracted (and therefore counted in @c gcount()) but not stored
   406	       *  -# @c __n-1 characters are stored, in which case failbit is set
   407	       *     in the stream error state
   408	       *
   409	       *  If no characters are extracted, failbit is set.  (An empty line of
   410	       *  input should therefore not cause failbit to be set.)
   411	       *
   412	       *  In any case, a null character is stored in the next location in
   413	       *  the array.
   414	      */
   415	      __istream_type&
   416	      getline(char_type* __s, streamsize __n, char_type __delim);
   417	
   418	      /**
   419	       *  @brief  String extraction.
   420	       *  @param  __s  A character array in which to store the data.
   421	       *  @param  __n  Maximum number of characters to extract.
   422	       *  @return  *this
   423	       *
   424	       *  Returns @c getline(__s,__n,widen('\\n')).
   425	      */
   426	      __istream_type&
   427	      getline(char_type* __s, streamsize __n)
   428	      { return this->getline(__s, __n, this->widen('\n')); }
   429	
   430	      /**
   431	       *  @brief  Discarding characters
   432	       *  @param  __n  Number of characters to discard.
   433	       *  @param  __delim  A "stop" character.
   434	       *  @return  *this
   435	       *
   436	       *  Extracts characters and throws them away until one of the
   437	       *  following happens:
   438	       *  - if @a __n @c != @c std::numeric_limits<int>::max(), @a __n
   439	       *    characters are extracted
   440	       *  - the input sequence reaches end-of-file
   441	       *  - the next character equals @a __delim (in this case, the character
   442	       *    is extracted); note that this condition will never occur if
   443	       *    @a __delim equals @c traits::eof().
   444	       *
   445	       *  NB: Provide three overloads, instead of the single function
   446	       *  (with defaults) mandated by the Standard: this leads to a
   447	       *  better performing implementation, while still conforming to
   448	       *  the Standard.
   449	      */
   450	      __istream_type&
   451	      ignore(streamsize __n, int_type __delim);
   452	
   453	      __istream_type&
   454	      ignore(streamsize __n);
   455	
   456	      __istream_type&
   457	      ignore();
   458	
   459	      /**
   460	       *  @brief  Looking ahead in the stream
   461	       *  @return  The next character, or eof().
   462	       *
   463	       *  If, after constructing the sentry object, @c good() is false,
   464	       *  returns @c traits::eof().  Otherwise reads but does not extract
   465	       *  the next input character.
   466	      */
   467	      int_type
   468	      peek();
   469	
   470	      /**
   471	       *  @brief  Extraction without delimiters.
   472	       *  @param  __s  A character array.
   473	       *  @param  __n  Maximum number of characters to store.
   474	       *  @return  *this
   475	       *
   476	       *  If the stream state is @c good(), extracts characters and stores
   477	       *  them into @a __s until one of the following happens:
   478	       *  - @a __n characters are stored
   479	       *  - the input sequence reaches end-of-file, in which case the error
   480	       *    state is set to @c failbit|eofbit.
   481	       *
   482	       *  @note  This function is not overloaded on signed char and
   483	       *         unsigned char.
   484	      */
   485	      __istream_type&
   486	      read(char_type* __s, streamsize __n);
   487	
   488	      /**
   489	       *  @brief  Extraction until the buffer is exhausted, but no more.
   490	       *  @param  __s  A character array.
   491	       *  @param  __n  Maximum number of characters to store.
   492	       *  @return  The number of characters extracted.
   493	       *
   494	       *  Extracts characters and stores them into @a __s depending on the
   495	       *  number of characters remaining in the streambuf's buffer,
   496	       *  @c rdbuf()->in_avail(), called @c A here:
   497	       *  - if @c A @c == @c -1, sets eofbit and extracts no characters
   498	       *  - if @c A @c == @c 0, extracts no characters
   499	       *  - if @c A @c > @c 0, extracts @c min(A,n)
   500	       *
   501	       *  The goal is to empty the current buffer, and to not request any
   502	       *  more from the external input sequence controlled by the streambuf.
   503	      */
   504	      streamsize
   505	      readsome(char_type* __s, streamsize __n);
   506	
   507	      /**
   508	       *  @brief  Unextracting a single character.
   509	       *  @param  __c  The character to push back into the input stream.
   510	       *  @return  *this
   511	       *
   512	       *  If @c rdbuf() is not null, calls @c rdbuf()->sputbackc(c).
   513	       *
   514	       *  If @c rdbuf() is null or if @c sputbackc() fails, sets badbit in
   515	       *  the error state.
   516	       *
   517	       *  @note  This function first clears eofbit.  Since no characters
   518	       *         are extracted, the next call to @c gcount() will return 0,
   519	       *         as required by DR 60.
   520	      */
   521	      __istream_type&
   522	      putback(char_type __c);
   523	
   524	      /**
   525	       *  @brief  Unextracting the previous character.
   526	       *  @return  *this
   527	       *
   528	       *  If @c rdbuf() is not null, calls @c rdbuf()->sungetc(c).
   529	       *
   530	       *  If @c rdbuf() is null or if @c sungetc() fails, sets badbit in
   531	       *  the error state.
   532	       *
   533	       *  @note  This function first clears eofbit.  Since no characters
   534	       *         are extracted, the next call to @c gcount() will return 0,
   535	       *         as required by DR 60.
   536	      */
   537	      __istream_type&
   538	      unget();
   539	
   540	      /**
   541	       *  @brief  Synchronizing the stream buffer.
   542	       *  @return  0 on success, -1 on failure
   543	       *
   544	       *  If @c rdbuf() is a null pointer, returns -1.
   545	       *
   546	       *  Otherwise, calls @c rdbuf()->pubsync(), and if that returns -1,
   547	       *  sets badbit and returns -1.
   548	       *
   549	       *  Otherwise, returns 0.
   550	       *
   551	       *  @note  This function does not count the number of characters
   552	       *         extracted, if any, and therefore does not affect the next
   553	       *         call to @c gcount().
   554	      */
   555	      int
   556	      sync();
   557	
   558	      /**
   559	       *  @brief  Getting the current read position.
   560	       *  @return  A file position object.
   561	       *
   562	       *  If @c fail() is not false, returns @c pos_type(-1) to indicate
   563	       *  failure.  Otherwise returns @c rdbuf()->pubseekoff(0,cur,in).
   564	       *
   565	       *  @note  This function does not count the number of characters
   566	       *         extracted, if any, and therefore does not affect the next
   567	       *         call to @c gcount().  At variance with putback, unget and
   568	       *         seekg, eofbit is not cleared first.
   569	      */
   570	      pos_type
   571	      tellg();
   572	
   573	      /**
   574	       *  @brief  Changing the current read position.
   575	       *  @param  __pos  A file position object.
   576	       *  @return  *this
   577	       *
   578	       *  If @c fail() is not true, calls @c rdbuf()->pubseekpos(__pos).  If
   579	       *  that function fails, sets failbit.
   580	       *
   581	       *  @note  This function first clears eofbit.  It does not count the
   582	       *         number of characters extracted, if any, and therefore does
   583	       *         not affect the next call to @c gcount().
   584	      */
   585	      __istream_type&
   586	      seekg(pos_type);
   587	
   588	      /**
   589	       *  @brief  Changing the current read position.
   590	       *  @param  __off  A file offset object.
   591	       *  @param  __dir  The direction in which to seek.
   592	       *  @return  *this
   593	       *
   594	       *  If @c fail() is not true, calls @c rdbuf()->pubseekoff(__off,__dir).
   595	       *  If that function fails, sets failbit.
   596	       *
   597	       *  @note  This function first clears eofbit.  It does not count the
   598	       *         number of characters extracted, if any, and therefore does
   599	       *         not affect the next call to @c gcount().
   600	      */
   601	      __istream_type&
   602	      seekg(off_type, ios_base::seekdir);
   603	      ///@}
   604	
   605	    protected:
   606	      basic_istream()
   607	      : _M_gcount(streamsize(0))
   608	      { this->init(0); }
   609	
   610	#if __cplusplus >= 201103L
   611	      basic_istream(const basic_istream&) = delete;
   612	
   613	      basic_istream(basic_istream&& __rhs)
   614	      : __ios_type(), _M_gcount(__rhs._M_gcount)
   615	      {
   616		__ios_type::move(__rhs);
   617		__rhs._M_gcount = 0;
   618	      }
   619	
   620	      // 27.7.3.3 Assign/swap
   621	
   622	      basic_istream& operator=(const basic_istream&) = delete;
   623	
   624	      basic_istream&
   625	      operator=(basic_istream&& __rhs)
   626	      {
   627		swap(__rhs);
   628		return *this;
   629	      }
   630	
   631	      void
   632	      swap(basic_istream& __rhs)
   633	      {
   634		__ios_type::swap(__rhs);
   635		std::swap(_M_gcount, __rhs._M_gcount);
   636	      }
   637	#endif
   638	
   639	      template<typename _ValueT>
   640		__istream_type&
   641		_M_extract(_ValueT& __v);
   642	    };
   643	
   644	  /// Explicit specialization declarations, defined in src/istream.cc.
   645	  template<>
   646	    basic_istream<char>&
   647	    basic_istream<char>::
   648	    getline(char_type* __s, streamsize __n, char_type __delim);
   649	
   650	  template<>
   651	    basic_istream<char>&
   652	    basic_istream<char>::
   653	    ignore(streamsize __n);
   654	
   655	  template<>
   656	    basic_istream<char>&
   657	    basic_istream<char>::
   658	    ignore(streamsize __n, int_type __delim);
   659	
   660	#ifdef _GLIBCXX_USE_WCHAR_T
   661	  template<>
   662	    basic_istream<wchar_t>&
   663	    basic_istream<wchar_t>::
   664	    getline(char_type* __s, streamsize __n, char_type __delim);
   665	
   666	  template<>
   667	    basic_istream<wchar_t>&
   668	    basic_istream<wchar_t>::
   669	    ignore(streamsize __n);
   670	
   671	  template<>
   672	    basic_istream<wchar_t>&
   673	    basic_istream<wchar_t>::
   674	    ignore(streamsize __n, int_type __delim);
   675	#endif
   676	
   677	  /**
   678	   *  @brief  Performs setup work for input streams.
   679	   *
   680	   *  Objects of this class are created before all of the standard
   681	   *  extractors are run.  It is responsible for <em>exception-safe
   682	   *  prefix and suffix operations,</em> although only prefix actions
   683	   *  are currently required by the standard.
   684	  */
   685	  template<typename _CharT, typename _Traits>
   686	    class basic_istream<_CharT, _Traits>::sentry
   687	    {
   688	      // Data Members.
   689	      bool _M_ok;
   690	
   691	    public:
   692	      /// Easy access to dependent types.
   693	      typedef _Traits 					traits_type;
   694	      typedef basic_streambuf<_CharT, _Traits> 		__streambuf_type;
   695	      typedef basic_istream<_CharT, _Traits> 		__istream_type;
   696	      typedef typename __istream_type::__ctype_type 	__ctype_type;
   697	      typedef typename _Traits::int_type		__int_type;
   698	
   699	      /**
   700	       *  @brief  The constructor performs all the work.
   701	       *  @param  __is  The input stream to guard.
   702	       *  @param  __noskipws  Whether to consume whitespace or not.
   703	       *
   704	       *  If the stream state is good (@a __is.good() is true), then the
   705	       *  following actions are performed, otherwise the sentry state
   706	       *  is false (<em>not okay</em>) and failbit is set in the
   707	       *  stream state.
   708	       *
   709	       *  The sentry's preparatory actions are:
   710	       *
   711	       *  -# if the stream is tied to an output stream, @c is.tie()->flush()
   712	       *     is called to synchronize the output sequence
   713	       *  -# if @a __noskipws is false, and @c ios_base::skipws is set in
   714	       *     @c is.flags(), the sentry extracts and discards whitespace
   715	       *     characters from the stream.  The currently imbued locale is
   716	       *     used to determine whether each character is whitespace.
   717	       *
   718	       *  If the stream state is still good, then the sentry state becomes
   719	       *  true (@a okay).
   720	      */
   721	      explicit
   722	      sentry(basic_istream<_CharT, _Traits>& __is, bool __noskipws = false);
   723	
   724	      /**
   725	       *  @brief  Quick status checking.
   726	       *  @return  The sentry state.
   727	       *
   728	       *  For ease of use, sentries may be converted to booleans.  The
   729	       *  return value is that of the sentry state (true == okay).
   730	      */
   731	#if __cplusplus >= 201103L
   732	      explicit
   733	#endif
   734	      operator bool() const
   735	      { return _M_ok; }
   736	    };
   737	
   738	  ///@{
   739	  /**
   740	   *  @brief  Character extractors
   741	   *  @param  __in  An input stream.
   742	   *  @param  __c  A character reference.
   743	   *  @return  in
   744	   *
   745	   *  Behaves like one of the formatted arithmetic extractors described in
   746	   *  std::basic_istream.  After constructing a sentry object with good
   747	   *  status, this function extracts a character (if one is available) and
   748	   *  stores it in @a __c.  Otherwise, sets failbit in the input stream.
   749	  */
   750	  template<typename _CharT, typename _Traits>
   751	    basic_istream<_CharT, _Traits>&
   752	    operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c);
   753	
   754	  template<class _Traits>
   755	    inline basic_istream<char, _Traits>&
   756	    operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
   757	    { return (__in >> reinterpret_cast<char&>(__c)); }
   758	
   759	  template<class _Traits>
   760	    inline basic_istream<char, _Traits>&
   761	    operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
   762	    { return (__in >> reinterpret_cast<char&>(__c)); }
   763	  ///@}
   764	
   765	
   766	  template<typename _CharT, typename _Traits>
   767	    void
   768	    __istream_extract(basic_istream<_CharT, _Traits>&, _CharT*, streamsize);
   769	
   770	  void __istream_extract(istream&, char*, streamsize);
   771	
   772	  ///@{
   773	  /**
   774	   *  @brief  Character string extractors
   775	   *  @param  __in  An input stream.
   776	   *  @param  __s  A character array (or a pointer to an array before C++20).
   777	   *  @return  __in
   778	   *
   779	   *  Behaves like one of the formatted arithmetic extractors described in
   780	   *  `std::basic_istream`.  After constructing a sentry object with good
   781	   *  status, this function extracts up to `n` characters and stores them
   782	   *  into the array `__s`.  `n` is defined as:
   783	   *
   784	   *  - if `width()` is greater than zero, `n` is `min(width(), n)`
   785	   *  - otherwise `n` is the number of elements of the array
   786	   *  - (before C++20 the pointer is assumed to point to an array of
   787	   *    the largest possible size for an array of `char_type`).
   788	   *
   789	   *  Characters are extracted and stored until one of the following happens:
   790	   *  - `n - 1` characters are stored
   791	   *  - EOF is reached
   792	   *  - the next character is whitespace according to the current locale
   793	   *
   794	   *  `width(0)` is then called for the input stream.
   795	   *
   796	   *  If no characters are extracted, sets failbit.
   797	  */
   798	
   799	#if __cplusplus <= 201703L
   800	  template<typename _CharT, typename _Traits>
   801	    __attribute__((__nonnull__(2), __access__(__write_only__, 2)))
   802	    inline basic_istream<_CharT, _Traits>&
   803	    operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
   804	    {
   805	#ifdef __OPTIMIZE__
   806	      // Function inlining might make the buffer size known, allowing us to
   807	      // prevent overflow.
   808	      size_t __n = __builtin_object_size(__s, 0);
   809	      if (__n < sizeof(_CharT))
   810		{
   811		  // There is not even space for the required null terminator.
   812		  __glibcxx_assert(__n >= sizeof(_CharT));
   813		  // No point calling __istream_extract, but still need to reset width.
   814		  __in.width(0);
   815		  __in.setstate(ios_base::failbit);
   816		}
   817	      else if (__n != (size_t)-1)
   818		{
   819		  __n /= sizeof(_CharT);
   820		  streamsize __w = __in.width();
   821		  std::__istream_extract(__in, __s, __n);
   822		  if (__in.good() && (__w <= 0 || __n < __w))
   823		    {
   824		      // Stopped extracting early to avoid overflowing the buffer,
   825		      // but might have stopped anyway (and set eofbit) if at EOF.
   826		      const typename _Traits::int_type __c = __in.rdbuf()->sgetc();
   827		      const bool __eof = _Traits::eq_int_type(__c, _Traits::eof());
   828		      if (__builtin_expect(__eof, true)) // Assume EOF, not overflow.
   829			__in.setstate(ios_base::eofbit);
   830		    }
   831		}
   832	      else
   833	#endif // __OPTIMIZE
   834		{
   835		  // Buffer size is unknown, have to assume it's huge.
   836		  streamsize __n = __gnu_cxx::__numeric_traits<streamsize>::__max;
   837		  __n /= sizeof(_CharT);
   838		  std::__istream_extract(__in, __s, __n);
   839		}
   840	      return __in;
   841	    }
   842	
   843	  template<class _Traits>
   844	    __attribute__((__nonnull__(2), __access__(__write_only__, 2)))
   845	    inline basic_istream<char, _Traits>&
   846	    operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
   847	    { return __in >> reinterpret_cast<char*>(__s); }
   848	
   849	  template<class _Traits>
   850	    __attribute__((__nonnull__(2), __access__(__write_only__, 2)))
   851	    inline basic_istream<char, _Traits>&
   852	    operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
   853	    { return __in >> reinterpret_cast<char*>(__s); }
   854	#else
   855	  // _GLIBCXX_RESOLVE_LIB_DEFECTS
   856	  // 2499. operator>>(istream&, char*) makes it hard to avoid buffer overflows
   857	  template<typename _CharT, typename _Traits, size_t _Num>
   858	    inline basic_istream<_CharT, _Traits>&
   859	    operator>>(basic_istream<_CharT, _Traits>& __in, _CharT (&__s)[_Num])
   860	    {
   861	      static_assert(_Num <= __gnu_cxx::__numeric_traits<streamsize>::__max);
   862	      std::__istream_extract(__in, __s, _Num);
   863	      return __in;
   864	    }
   865	
   866	  template<class _Traits, size_t _Num>
   867	    inline basic_istream<char, _Traits>&
   868	    operator>>(basic_istream<char, _Traits>& __in, unsigned char (&__s)[_Num])
   869	    { return __in >> reinterpret_cast<char(&)[_Num]>(__s); }
   870	
   871	  template<class _Traits, size_t _Num>
   872	    inline basic_istream<char, _Traits>&
   873	    operator>>(basic_istream<char, _Traits>& __in, signed char (&__s)[_Num])
   874	    { return __in >> reinterpret_cast<char(&)[_Num]>(__s); }
   875	#endif
   876	  ///@}
   877	
   878	  /**
   879	   *  @brief  Template class basic_iostream
   880	   *  @ingroup io
   881	   *
   882	   *  @tparam _CharT  Type of character stream.
   883	   *  @tparam _Traits  Traits for character type, defaults to
   884	   *                   char_traits<_CharT>.
   885	   *
   886	   *  This class multiply inherits from the input and output stream classes
   887	   *  simply to provide a single interface.
   888	  */
   889	  template<typename _CharT, typename _Traits>
   890	    class basic_iostream
   891	    : public basic_istream<_CharT, _Traits>,
   892	      public basic_ostream<_CharT, _Traits>
   893	    {
   894	    public:
   895	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
   896	      // 271. basic_iostream missing typedefs
   897	      // Types (inherited):
   898	      typedef _CharT			 		char_type;
   899	      typedef typename _Traits::int_type 		int_type;
   900	      typedef typename _Traits::pos_type 		pos_type;
   901	      typedef typename _Traits::off_type 		off_type;
   902	      typedef _Traits			 		traits_type;
   903	
   904	      // Non-standard Types:
   905	      typedef basic_istream<_CharT, _Traits>		__istream_type;
   906	      typedef basic_ostream<_CharT, _Traits>		__ostream_type;
   907	
   908	      /**
   909	       *  @brief  Constructor does nothing.
   910	       *
   911	       *  Both of the parent classes are initialized with the same
   912	       *  streambuf pointer passed to this constructor.
   913	      */
   914	      explicit
   915	      basic_iostream(basic_streambuf<_CharT, _Traits>* __sb)
   916	      : __istream_type(__sb), __ostream_type(__sb) { }
   917	
   918	      /**
   919	       *  @brief  Destructor does nothing.
   920	      */
   921	      virtual
   922	      ~basic_iostream() { }
   923	
   924	    protected:
   925	      basic_iostream()
   926	      : __istream_type(), __ostream_type() { }
   927	
   928	#if __cplusplus >= 201103L
   929	      basic_iostream(const basic_iostream&) = delete;
   930	
   931	      basic_iostream(basic_iostream&& __rhs)
   932	      : __istream_type(std::move(__rhs)), __ostream_type(*this)
   933	      { }
   934	
   935	      // 27.7.3.3 Assign/swap
   936	
   937	      basic_iostream& operator=(const basic_iostream&) = delete;
   938	
   939	      basic_iostream&
   940	      operator=(basic_iostream&& __rhs)
   941	      {
   942		swap(__rhs);
   943		return *this;
   944	      }
   945	
   946	      void
   947	      swap(basic_iostream& __rhs)
   948	      { __istream_type::swap(__rhs); }
   949	#endif
   950	    };
   951	
   952	  /**
   953	   *  @brief  Quick and easy way to eat whitespace
   954	   *
   955	   *  This manipulator extracts whitespace characters, stopping when the
   956	   *  next character is non-whitespace, or when the input sequence is empty.
   957	   *  If the sequence is empty, @c eofbit is set in the stream, but not
   958	   *  @c failbit.
   959	   *
   960	   *  The current locale is used to distinguish whitespace characters.
   961	   *
   962	   *  Example:
   963	   *  @code
   964	   *     MyClass   mc;
   965	   *
   966	   *     std::cin >> std::ws >> mc;
   967	   *  @endcode
   968	   *  will skip leading whitespace before calling operator>> on cin and your
   969	   *  object.  Note that the same effect can be achieved by creating a
   970	   *  std::basic_istream::sentry inside your definition of operator>>.
   971	  */
   972	  template<typename _CharT, typename _Traits>
   973	    basic_istream<_CharT, _Traits>&
   974	    ws(basic_istream<_CharT, _Traits>& __is);
   975	
   976	#if __cplusplus >= 201103L
   977	  // C++11 27.7.2.6 Rvalue stream extraction [istream.rvalue]
   978	  // _GLIBCXX_RESOLVE_LIB_DEFECTS
   979	  // 2328. Rvalue stream extraction should use perfect forwarding
   980	  // 1203. More useful rvalue stream insertion
   981	
   982	#if __cpp_lib_concepts
   983	  template<typename _Is, typename _Tp>
   984	    requires __derived_from_ios_base<_Is>
   985	      && requires (_Is& __is, _Tp&& __t) { __is >> std::forward<_Tp>(__t); }
   986	    using __rvalue_stream_extraction_t = _Is&&;
   987	#else
   988	  template<typename _Is, typename _Tp,
   989		   typename = _Require_derived_from_ios_base<_Is>,
   990		   typename = decltype(std::declval<_Is&>() >> std::declval<_Tp>())>
   991	    using __rvalue_stream_extraction_t = _Is&&;
   992	#endif
   993	
   994	  /**
   995	   *  @brief  Generic extractor for rvalue stream
   996	   *  @param  __is  An input stream.
   997	   *  @param  __x  A reference to the extraction target.
   998	   *  @return  __is
   999	   *
  1000	   *  This is just a forwarding function to allow extraction from
  1001	   *  rvalue streams since they won't bind to the extractor functions
  1002	   *  that take an lvalue reference.
  1003	  */
  1004	  template<typename _Istream, typename _Tp>
  1005	    inline __rvalue_stream_extraction_t<_Istream, _Tp>
  1006	    operator>>(_Istream&& __is, _Tp&& __x)
  1007	    {
  1008	      __is >> std::forward<_Tp>(__x);
  1009	      return std::move(__is);
  1010	    }
  1011	#endif // C++11
  1012	
  1013	_GLIBCXX_END_NAMESPACE_VERSION
  1014	} // namespace
  1015	
  1016	#include <bits/istream.tcc>
  1017	
  1018	#endif	/* _GLIBCXX_ISTREAM */