头文件<limits.h>用来检测整型数据类型的表达式范围。
Linux version 2.6.32-573.el6.x86_64中<limits.h>源码：
/* Copyright (C) 1991, 1992, 1996, 1997, 1998, 1999, 2000, 2005
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. */
/*
* ISO C99 Standard: 7.10/5.2.4.2.1 Sizes of integer types <limits.h>
*/
#ifndef _LIBC_LIMITS_H_
#define _LIBC_LIMITS_H_ 1
#include <features.h>
/* Maximum length of any multibyte character in any locale.
We define this value here since the gcc header does not define
the correct value. */
#define MB_LEN_MAX 16
/* If we are not using GNU CC we have to define all the symbols ourself.
Otherwise use gcc's definitions (see below). */
#if !defined __GNUC__ || __GNUC__ < 2
/* We only protect from multiple inclusion here, because all the other
#include's protect themselves, and in GCC 2 we may #include_next through
multiple copies of this file before we get to GCC's. */
# ifndef _LIMITS_H
# define _LIMITS_H 1
#include <bits/wordsize.h>
/* We don't have #include_next.
Define ANSI <limits.h> for standard 32-bit words. */
/* These assume 8-bit `char's, 16-bit `short int's,
and 32-bit `int's and `long int's. */
/* Number of bits in a `char'. */
# define CHAR_BIT 8
/* Minimum and maximum values a `signed char' can hold. */
# define SCHAR_MIN (-128)
# define SCHAR_MAX 127
/* Maximum value an `unsigned char' can hold. (Minimum is 0.) */
# define UCHAR_MAX 255
/* Minimum and maximum values a `char' can hold. */
# ifdef __CHAR_UNSIGNED__
# define CHAR_MIN 0
# define CHAR_MAX UCHAR_MAX
# else
# define CHAR_MIN SCHAR_MIN
# define CHAR_MAX SCHAR_MAX
# endif
/* Minimum and maximum values a `signed short int' can hold. */
# define SHRT_MIN (-32768)
# define SHRT_MAX 32767
/* Maximum value an `unsigned short int' can hold. (Minimum is 0.) */
# define USHRT_MAX 65535
/* Minimum and maximum values a `signed int' can hold. */
# define INT_MIN (-INT_MAX - 1)
# define INT_MAX 2147483647
/* Maximum value an `unsigned int' can hold. (Minimum is 0.) */
# define UINT_MAX 4294967295U
/* Minimum and maximum values a `signed long int' can hold. */
# if __WORDSIZE == 64
# define LONG_MAX 9223372036854775807L
# else
# define LONG_MAX 2147483647L
# endif
# define LONG_MIN (-LONG_MAX - 1L)
/* Maximum value an `unsigned long int' can hold. (Minimum is 0.) */
# if __WORDSIZE == 64
# define ULONG_MAX 18446744073709551615UL
# else
# define ULONG_MAX 4294967295UL
# endif
# ifdef __USE_ISOC99
/* Minimum and maximum values a `signed long long int' can hold. */
# define LLONG_MAX 9223372036854775807LL
# define LLONG_MIN (-LLONG_MAX - 1LL)
/* Maximum value an `unsigned long long int' can hold. (Minimum is 0.) */
# define ULLONG_MAX 18446744073709551615ULL
# endif /* ISO C99 */
# endif /* limits.h */
#endif /* GCC 2. */
#endif /* !_LIBC_LIMITS_H_ */
/* Get the compiler's limits.h, which defines almost all the ISO constants.
We put this #include_next outside the double inclusion check because
it should be possible to include this file more than once and still get
the definitions from gcc's header. */
#if defined __GNUC__ && !defined _GCC_LIMITS_H_
/* `_GCC_LIMITS_H_' is what GCC's file defines. */
# include_next <limits.h>
#endif
/* The <limits.h> files in some gcc versions don't define LLONG_MIN,
LLONG_MAX, and ULLONG_MAX. Instead only the values gcc defined for
ages are available. */
#if defined __USE_ISOC99 && defined __GNUC__
# ifndef LLONG_MIN
# define LLONG_MIN (-LLONG_MAX-1)
# endif
# ifndef LLONG_MAX
# define LLONG_MAX __LONG_LONG_MAX__
# endif
# ifndef ULLONG_MAX
# define ULLONG_MAX (LLONG_MAX * 2ULL + 1)
# endif
#endif
#ifdef __USE_POSIX
/* POSIX adds things to <limits.h>. */
# include <bits/posix1_lim.h>
#endif
#ifdef __USE_POSIX2
# include <bits/posix2_lim.h>
#endif
#ifdef __USE_XOPEN
# include <bits/xopen_lim.h>
#endif
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