The C and C++ Include Header Files

/usr/include/x86_64-linux-gnu/bits/select2.h


$ cat -n /usr/include/x86_64-linux-gnu/bits/select2.h

     1	/* Checking macros for select functions.
     2	   Copyright (C) 2011-2024 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_SELECT_H
    20	# error "Never include <bits/select2.h> directly; use <sys/select.h> instead."
    21	#endif
    22	
    23	#include <bits/select-decl.h>
    24	
    25	#undef __FD_ELT
    26	#define	__FD_ELT(d) \
    27	  __extension__								    \
    28	  ({ long int __d = (d);						    \
    29	     (__builtin_constant_p (__d)					    \
    30	      ? (0 <= __d && __d < __FD_SETSIZE					    \
    31		 ? (__d / __NFDBITS)						    \
    32		 : __fdelt_warn (__d))						    \
    33	      : __fdelt_chk (__d)); })