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The C and C++ Include Header Files

cat -n /usr/include/c++/15/iostream

     1	// Standard iostream objects -*- C++ -*-
     2	
     3	// Copyright (C) 1997-2025 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	/** @file include/iostream
    26	 *  This is a Standard C++ Library header.
    27	 */
    28	
    29	//
    30	// ISO C++ 14882: 27.3  Standard iostream objects
    31	//
    32	
    33	#ifndef _GLIBCXX_IOSTREAM
    34	#define _GLIBCXX_IOSTREAM 1
    35	
    36	#ifdef _GLIBCXX_SYSHDR
    37	#pragma GCC system_header
    38	#endif
    39	
    40	#include <bits/requires_hosted.h> // iostreams
    41	
    42	#include <bits/c++config.h>
    43	#include <ostream>
    44	#include <istream>
    45	
    46	namespace std _GLIBCXX_VISIBILITY(default)
    47	{
    48	_GLIBCXX_BEGIN_NAMESPACE_VERSION
    49	
    50	  /**
    51	   *  @name Standard Stream Objects
    52	   *
    53	   *  The `<iostream>` header declares the eight *standard stream objects*.
    54	   *  For other declarations, see
    55	   *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/io.html
    56	   *  and the @link iosfwd I/O forward declarations @endlink
    57	   *
    58	   *  They are required by default to cooperate with the global C
    59	   *  library's `FILE` streams, and to be available during program
    60	   *  startup and termination. For more information, see the section of the
    61	   *  manual linked to above.
    62	  */
    63	  ///@{
    64	  extern istream cin;		///< Linked to standard input
    65	  extern ostream cout;		///< Linked to standard output
    66	  extern ostream cerr;		///< Linked to standard error (unbuffered)
    67	  extern ostream clog;		///< Linked to standard error (buffered)
    68	
    69	#ifdef _GLIBCXX_USE_WCHAR_T
    70	  extern wistream wcin;		///< Linked to standard input
    71	  extern wostream wcout;	///< Linked to standard output
    72	  extern wostream wcerr;	///< Linked to standard error (unbuffered)
    73	  extern wostream wclog;	///< Linked to standard error (buffered)
    74	#endif
    75	  ///@}
    76	
    77	  // For construction of filebuffers for cout, cin, cerr, clog et. al.
    78	  // When the init_priority attribute is usable, we do this initialization
    79	  // in the compiled library instead (src/c++98/globals_io.cc).
    80	#if !(_GLIBCXX_USE_INIT_PRIORITY_ATTRIBUTE \
    81	      && __has_attribute(__init_priority__))
    82	  static ios_base::Init __ioinit;
    83	#elif defined(_GLIBCXX_SYMVER_GNU) && defined(__ELF__)
    84	  __extension__ __asm (".globl _ZSt21ios_base_library_initv");
    85	#endif
    86	
    87	_GLIBCXX_END_NAMESPACE_VERSION
    88	} // namespace
    89	
    90	#endif /* _GLIBCXX_IOSTREAM */