sysconf.c

glibc 库, 不仅可以学习使用库函数,还可以学习函数的具体实现,是提高功力的好资料

/* Get file-specific information about a file.  Linux version.
   Copyright (C) 2003, 2004 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <stdbool.h>
#include <stdlib.h>
#include <unistd.h>


#include "has_cpuclock.c"

static long int linux_sysconf (int name);


/* Get the value of the system variable NAME.  */
long int
__sysconf (int name)
{
  if (name == _SC_CPUTIME || name == _SC_THREAD_CPUTIME)
    return has_cpuclock () ? 200112L : -1;

  /* Everything else is handled by the more general code.  */
  return linux_sysconf (name);
}

/* Now the generic Linux version.  */
#undef __sysconf
#define __sysconf static linux_sysconf
#include "../sysconf.c"