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The C and C++ Include Header Files

cat -n /usr/include/c++/15/complex.h

     1	// -*- C++ -*- compatibility header.
     2	
     3	// Copyright (C) 2007-2025 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 complex.h
    26	 *  This is a Standard C++ Library header.
    27	 */
    28	
    29	#ifndef _GLIBCXX_COMPLEX_H
    30	#define _GLIBCXX_COMPLEX_H 1
    31	
    32	#include <bits/c++config.h>
    33	
    34	#if __cplusplus >= 201103L
    35	extern "C++" {
    36	#include <complex>
    37	}
    38	#endif
    39	
    40	#if __cplusplus >= 201103L && defined(__STRICT_ANSI__)
    41	// For strict modes do not include the C library's <complex.h>, see PR 82417.
    42	#elif _GLIBCXX_HAVE_COMPLEX_H
    43	# include_next <complex.h>
    44	# ifdef _GLIBCXX_COMPLEX
    45	// See PR56111, keep the macro in C++03 if possible.
    46	#  undef complex
    47	# endif
    48	#endif
    49	
    50	#endif