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The C and C++ Include Header Files

cat -n /usr/include/x86_64-linux-gnu/bits/ipctypes.h

     1	/* bits/ipctypes.h -- Define some types used by SysV IPC/MSG/SHM.
     2	   Copyright (C) 2012-2026 Free Software Foundation, Inc.
     3	   This file is part of the GNU C Library.
     4	
     5	   The GNU C Library is free software; you can redistribute it and/or
     6	   modify it under the terms of the GNU Lesser General Public
     7	   License as published by the Free Software Foundation; either
     8	   version 2.1 of the License, or (at your option) any later version.
     9	
    10	   The GNU C Library is distributed in the hope that it will be useful,
    11	   but WITHOUT ANY WARRANTY; without even the implied warranty of
    12	   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    13	   Lesser General Public License for more details.
    14	
    15	   You should have received a copy of the GNU Lesser General Public
    16	   License along with the GNU C Library; if not, see
    17	   <https://www.gnu.org/licenses/>.  */
    18	
    19	#ifndef _SYS_IPC_H
    20	# error "Never use <bits/ipctypes.h> directly; include <sys/ipc.h> instead."
    21	#endif
    22	
    23	#ifndef _BITS_IPCTYPES_H
    24	#define _BITS_IPCTYPES_H	1
    25	
    26	/* Used in `struct shmid_ds'.  */
    27	# ifdef __x86_64__
    28	typedef int __ipc_pid_t;
    29	# else
    30	typedef unsigned short int __ipc_pid_t;
    31	# endif
    32	
    33	#endif /* bits/ipctypes.h */