The C and C++ Include Header Files

/usr/include/regexp.h


$ cat -n /usr/include/regexp.h

     1	/* Copyright (C) 1996-2024 Free Software Foundation, Inc.
     2	   This file is part of the GNU C Library.
     3	
     4	   The GNU C Library is free software; you can redistribute it and/or
     5	   modify it under the terms of the GNU Lesser General Public
     6	   License as published by the Free Software Foundation; either
     7	   version 2.1 of the License, or (at your option) any later version.
     8	
     9	   The GNU C Library is distributed in the hope that it will be useful,
    10	   but WITHOUT ANY WARRANTY; without even the implied warranty of
    11	   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    12	   Lesser General Public License for more details.
    13	
    14	   You should have received a copy of the GNU Lesser General Public
    15	   License along with the GNU C Library; if not, see
    16	   <https://www.gnu.org/licenses/>.  */
    17	
    18	#ifndef _REGEXP_H
    19	#define _REGEXP_H	1
    20	
    21	/* The contents of this header file were originally standardized in
    22	   the Single Unix Specification, Issue 3 (1992).  In Issue 4 (1994)
    23	   the header was marked as TO BE WITHDRAWN, and new applications
    24	   were encouraged to use <regex.h> instead.  It was officially
    25	   withdrawn from the standard in Issue 6 (aka POSIX.1-2001).
    26	
    27	   The GNU C Library provided this header through version 2.22. */
    28	
    29	#error "The GNU C Library no longer implements <regexp.h>."
    30	#error "Please update your code to use <regex.h> instead (no trailing 'p')."
    31	
    32	#endif /* regexp.h */