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The C and C++ Include Header Files

cat -n /usr/include/x86_64-linux-gnu/c++/15/bits/os_defines.h

     1	// Specific definitions for GNU/Linux  -*- C++ -*-
     2	
     3	// Copyright (C) 2000-2025 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 bits/os_defines.h
    26	 *  This is an internal header file, included by other library headers.
    27	 *  Do not attempt to use it directly. @headername{iosfwd}
    28	 */
    29	
    30	#ifndef _GLIBCXX_OS_DEFINES
    31	#define _GLIBCXX_OS_DEFINES 1
    32	
    33	// System-specific #define, typedefs, corrections, etc, go here.  This
    34	// file will come before all others.
    35	
    36	// This keeps isalnum, et al from being propagated as macros.
    37	#define __NO_CTYPE 1
    38	
    39	#include <features.h>
    40	
    41	// Provide a declaration for the possibly deprecated gets function, as
    42	// glibc 2.15 and later does not declare gets for ISO C11 when
    43	// __GNU_SOURCE is defined.
    44	#if __GLIBC_PREREQ(2,15) && defined(_GNU_SOURCE)
    45	# undef _GLIBCXX_HAVE_GETS
    46	#endif
    47	
    48	// Glibc 2.23 removed the obsolete isinf and isnan declarations. Check the
    49	// version dynamically in case it has changed since libstdc++ was configured.
    50	#define _GLIBCXX_NO_OBSOLETE_ISINF_ISNAN_DYNAMIC __GLIBC_PREREQ(2,23)
    51	
    52	// Glibc 2.26 on i?86/x86-64/ia64/ppc64le added *f128 support.
    53	// Glibc 2.27 added it also on many other arches but those have IEEE quad
    54	// long double.
    55	#if __GLIBC_PREREQ(2, 26) \
    56	    && (defined(__i386__) || defined(__x86_64__) || defined (__ia64__) \
    57		|| (defined(__powerpc__) && defined(_ARCH_PWR8) \
    58		    && defined(__LITTLE_ENDIAN__) && (_CALL_ELF == 2) \
    59		    && defined(__FLOAT128__)))
    60	# define _GLIBCXX_HAVE_FLOAT128_MATH 1
    61	#endif
    62	
    63	// Enable __cxa_thread_atexit to rely on a (presumably libc-provided)
    64	// __cxa_thread_atexit_impl, if it happens to be defined, even if
    65	// configure couldn't find it during the build.
    66	#define _GLIBCXX_MAY_HAVE___CXA_THREAD_ATEXIT_IMPL 1
    67	
    68	#ifdef __linux__
    69	// The following libpthread properties only apply to Linux, not GNU/Hurd.
    70	
    71	# if __GLIBC_PREREQ(2, 27)
    72	// Since glibc 2.27 pthread_self() is usable without linking to libpthread.
    73	#  define _GLIBCXX_NATIVE_THREAD_ID pthread_self()
    74	# else
    75	// Before then it was in libc.so.6 but not libc.a, and always returns 0,
    76	// which breaks the invariant this_thread::get_id() != thread::id{}.
    77	// So only use it if we know the libpthread version is available.
    78	// Otherwise use (__gthread_t)1 as the ID of the main (and only) thread.
    79	#  define _GLIBCXX_NATIVE_THREAD_ID \
    80	   (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
    81	# endif
    82	
    83	# if __GLIBC_PREREQ(2, 34)
    84	// Since glibc 2.34 all pthreads functions are usable without linking to
    85	// libpthread.
    86	#  define _GLIBCXX_GTHREAD_USE_WEAK 0
    87	# endif
    88	#endif // __linux__
    89	
    90	#endif