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The C and C++ Include Header Files

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

     1	// -*- C++ -*- forwarding header.
     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/cctype
    26	 *  This is a Standard C++ Library file.  You should @c \#include this file
    27	 *  in your programs, rather than any of the @a *.h implementation files.
    28	 *
    29	 *  This is the C++ version of the Standard C Library header @c ctype.h,
    30	 *  and its contents are (mostly) the same as that header, but are all
    31	 *  contained in the namespace @c std (except for names which are defined
    32	 *  as macros in C).
    33	 */
    34	
    35	//
    36	// ISO C++ 14882: <ccytpe>
    37	//
    38	
    39	#ifndef _GLIBCXX_CCTYPE
    40	#define _GLIBCXX_CCTYPE 1
    41	
    42	#ifdef _GLIBCXX_SYSHDR
    43	#pragma GCC system_header
    44	#endif
    45	
    46	#include <bits/c++config.h>
    47	#include <ctype.h>
    48	
    49	// Get rid of those macros defined in <ctype.h> in lieu of real functions.
    50	#undef isalnum
    51	#undef isalpha
    52	#undef iscntrl
    53	#undef isdigit
    54	#undef isgraph
    55	#undef islower
    56	#undef isprint
    57	#undef ispunct
    58	#undef isspace
    59	#undef isupper
    60	#undef isxdigit
    61	#undef tolower
    62	#undef toupper
    63	
    64	namespace std
    65	{
    66	  using ::isalnum;
    67	  using ::isalpha;
    68	  using ::iscntrl;
    69	  using ::isdigit;
    70	  using ::isgraph;
    71	  using ::islower;
    72	  using ::isprint;
    73	  using ::ispunct;
    74	  using ::isspace;
    75	  using ::isupper;
    76	  using ::isxdigit;
    77	  using ::tolower;
    78	  using ::toupper;
    79	} // namespace std
    80	
    81	#if __cplusplus >= 201103L
    82	
    83	#ifdef _GLIBCXX_USE_C99_CTYPE
    84	
    85	#undef isblank
    86	
    87	namespace std
    88	{
    89	  using ::isblank;
    90	} // namespace std
    91	
    92	#endif // _GLIBCXX_USE_C99_CTYPE
    93	
    94	#endif // C++11
    95	
    96	#endif