最近在刷Leetcode的一些题的时候,发现经常会使用到最大值。在以前的学习过程中,只会知道java是有Integer.MAX_VALUE这样一个值,而且是在语言里定义的,java.lang.Integer.MAX_VALUE = 0x7FFFFFFF,那么在C++里怎么用才算方便呢?用 (1<<31)-1 会觉得比较奇怪,在代码中出现0x7FFFFFFF也是超级奇怪。那么这些值都是在哪些地方定义的呢?
在别人的代码中,见到了INT_MAX,那么这个值在哪里呢?
Xcode告诉我这个值在limits.h中
老版本的limit.h可能还会有NC++

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#define INT_MAX 2147483647

但是现在新的版本已经是

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#define INT_MAX __INT_MAX__

同样的 INT_MIN 、 LONG_MAX 等等数值都会有相应的定义。
使用Linux的G++也测试过了,都是一致的。

当然,这是基础的size的limits,还有一些内容并不是在limits.h中定义。
譬如使用Xcode时,很多内容的size,返回值也许不再是以前的int或者unsigned int了,而是size_t,而且size_t在32位系统中是32位,在64位系统中就变成了64位。
这个定义是SIZE_MAX在stdint.h

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#if __WORDSIZE == 64
#define SIZE_MAX UINT64_MAX
#else
#define SIZE_MAX UINT32_MAX
#endif
#define UINT8_MAX 255
#define UINT16_MAX 65535
#define UINT32_MAX 4294967295U
#define UINT64_MAX 18446744073709551615ULL

另外在这个文件内还定义了其他一些内容,譬如:

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#define INT8_MAX 127
#define INT16_MAX 32767
#define INT32_MAX 2147483647
#define INT64_MAX 9223372036854775807LL
#define INT8_MIN -128
#define INT16_MIN -32768
/*
Note: the literal "most negative int" cannot be written in C --
the rules in the standard (section 6.4.4.1 in C99) will give it
an unsigned type, so INT32_MIN (and the most negative member of
any larger signed type) must be written via a constant expression.
*/
#define INT32_MIN (-INT32_MAX-1)
#define INT64_MIN (-INT64_MAX-1)

使用g++也能测试通过。

附1:
超级简单的小测试

— filename: a.C –

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#include <iostream>
#include <limits.h>
#include <stdint.h>
using namespace std;
int main(){
cout << SIZE_MAX << endl;
cout << INT_MAX << endl;
cout << "Hello" << endl;
}

运行结果:

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18446744073709551615
2147483647
Hello

附2:
limits.h内容

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/*===---- limits.h - Standard header for integer sizes --------------------===*\
*
* Copyright (c) 2009 Chris Lattner
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*
\*===----------------------------------------------------------------------===*/
#ifndef __CLANG_LIMITS_H
#define __CLANG_LIMITS_H
/* The system's limits.h may, in turn, try to #include_next GCC's limits.h.
Avert this #include_next madness. */
#if defined __GNUC__ && !defined _GCC_LIMITS_H_
#define _GCC_LIMITS_H_
#endif
/* System headers include a number of constants from POSIX in <limits.h>.
Include it if we're hosted. */
#if __STDC_HOSTED__ && __has_include_next(<limits.h>)
#include_next <limits.h>
#endif
/* Many system headers try to "help us out" by defining these. No really, we
know how big each datatype is. */
#undef SCHAR_MIN
#undef SCHAR_MAX
#undef UCHAR_MAX
#undef SHRT_MIN
#undef SHRT_MAX
#undef USHRT_MAX
#undef INT_MIN
#undef INT_MAX
#undef UINT_MAX
#undef LONG_MIN
#undef LONG_MAX
#undef ULONG_MAX
#undef CHAR_BIT
#undef CHAR_MIN
#undef CHAR_MAX
/* C90/99 5.2.4.2.1 */
#define SCHAR_MAX __SCHAR_MAX__
#define SHRT_MAX __SHRT_MAX__
#define INT_MAX __INT_MAX__
#define LONG_MAX __LONG_MAX__
#define SCHAR_MIN (-__SCHAR_MAX__-1)
#define SHRT_MIN (-__SHRT_MAX__ -1)
#define INT_MIN (-__INT_MAX__ -1)
#define LONG_MIN (-__LONG_MAX__ -1L)
#define UCHAR_MAX (__SCHAR_MAX__*2 +1)
#define USHRT_MAX (__SHRT_MAX__ *2 +1)
#define UINT_MAX (__INT_MAX__ *2U +1U)
#define ULONG_MAX (__LONG_MAX__ *2UL+1UL)
#ifndef MB_LEN_MAX
#define MB_LEN_MAX 1
#endif
#define CHAR_BIT __CHAR_BIT__
#ifdef __CHAR_UNSIGNED__ /* -funsigned-char */
#define CHAR_MIN 0
#define CHAR_MAX UCHAR_MAX
#else
#define CHAR_MIN SCHAR_MIN
#define CHAR_MAX __SCHAR_MAX__
#endif
/* C99 5.2.4.2.1: Added long long.
C++11 18.3.3.2: same contents as the Standard C Library header <limits.h>.
*/
#if __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L
#undef LLONG_MIN
#undef LLONG_MAX
#undef ULLONG_MAX
#define LLONG_MAX __LONG_LONG_MAX__
#define LLONG_MIN (-__LONG_LONG_MAX__-1LL)
#define ULLONG_MAX (__LONG_LONG_MAX__*2ULL+1ULL)
#endif
/* LONG_LONG_MIN/LONG_LONG_MAX/ULONG_LONG_MAX are a GNU extension. It's too bad
that we don't have something like #pragma poison that could be used to
deprecate a macro - the code should just use LLONG_MAX and friends.
*/
#if defined(__GNU_LIBRARY__) ? defined(__USE_GNU) : !defined(__STRICT_ANSI__)
#undef LONG_LONG_MIN
#undef LONG_LONG_MAX
#undef ULONG_LONG_MAX
#define LONG_LONG_MAX __LONG_LONG_MAX__
#define LONG_LONG_MIN (-__LONG_LONG_MAX__-1LL)
#define ULONG_LONG_MAX (__LONG_LONG_MAX__*2ULL+1ULL)
#endif
#endif /* __CLANG_LIMITS_H */

附3:
stdint.h内容

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/*
* Copyright (c) 2000-2010 Apple Inc.
* All rights reserved.
*/
#ifndef _STDINT_H_
#define _STDINT_H_
#if __LP64__
#define __WORDSIZE 64
#else
#define __WORDSIZE 32
#endif
/* from ISO/IEC 988:1999 spec */
/* 7.18.1.1 Exact-width integer types */
#include <sys/_types/_int8_t.h>
#include <sys/_types/_int16_t.h>
#include <sys/_types/_int32_t.h>
#include <sys/_types/_int64_t.h>
#include <_types/_uint8_t.h>
#include <_types/_uint16_t.h>
#include <_types/_uint32_t.h>
#include <_types/_uint64_t.h>
/* 7.18.1.2 Minimum-width integer types */
typedef int8_t int_least8_t;
typedef int16_t int_least16_t;
typedef int32_t int_least32_t;
typedef int64_t int_least64_t;
typedef uint8_t uint_least8_t;
typedef uint16_t uint_least16_t;
typedef uint32_t uint_least32_t;
typedef uint64_t uint_least64_t;
/* 7.18.1.3 Fastest-width integer types */
typedef int8_t int_fast8_t;
typedef int16_t int_fast16_t;
typedef int32_t int_fast32_t;
typedef int64_t int_fast64_t;
typedef uint8_t uint_fast8_t;
typedef uint16_t uint_fast16_t;
typedef uint32_t uint_fast32_t;
typedef uint64_t uint_fast64_t;
/* 7.18.1.4 Integer types capable of holding object pointers */
#include <sys/_types.h>
#include <sys/_types/_intptr_t.h>
#include <sys/_types/_uintptr_t.h>
/* 7.18.1.5 Greatest-width integer types */
#include <_types/_intmax_t.h>
#include <_types/_uintmax_t.h>
/* 7.18.2 Limits of specified-width integer types:
* These #defines specify the minimum and maximum limits
* of each of the types declared above.
*/
/* 7.18.2.1 Limits of exact-width integer types */
#define INT8_MAX 127
#define INT16_MAX 32767
#define INT32_MAX 2147483647
#define INT64_MAX 9223372036854775807LL
#define INT8_MIN -128
#define INT16_MIN -32768
/*
Note: the literal "most negative int" cannot be written in C --
the rules in the standard (section 6.4.4.1 in C99) will give it
an unsigned type, so INT32_MIN (and the most negative member of
any larger signed type) must be written via a constant expression.
*/
#define INT32_MIN (-INT32_MAX-1)
#define INT64_MIN (-INT64_MAX-1)
#define UINT8_MAX 255
#define UINT16_MAX 65535
#define UINT32_MAX 4294967295U
#define UINT64_MAX 18446744073709551615ULL
/* 7.18.2.2 Limits of minimum-width integer types */
#define INT_LEAST8_MIN INT8_MIN
#define INT_LEAST16_MIN INT16_MIN
#define INT_LEAST32_MIN INT32_MIN
#define INT_LEAST64_MIN INT64_MIN
#define INT_LEAST8_MAX INT8_MAX
#define INT_LEAST16_MAX INT16_MAX
#define INT_LEAST32_MAX INT32_MAX
#define INT_LEAST64_MAX INT64_MAX
#define UINT_LEAST8_MAX UINT8_MAX
#define UINT_LEAST16_MAX UINT16_MAX
#define UINT_LEAST32_MAX UINT32_MAX
#define UINT_LEAST64_MAX UINT64_MAX
/* 7.18.2.3 Limits of fastest minimum-width integer types */
#define INT_FAST8_MIN INT8_MIN
#define INT_FAST16_MIN INT16_MIN
#define INT_FAST32_MIN INT32_MIN
#define INT_FAST64_MIN INT64_MIN
#define INT_FAST8_MAX INT8_MAX
#define INT_FAST16_MAX INT16_MAX
#define INT_FAST32_MAX INT32_MAX
#define INT_FAST64_MAX INT64_MAX
#define UINT_FAST8_MAX UINT8_MAX
#define UINT_FAST16_MAX UINT16_MAX
#define UINT_FAST32_MAX UINT32_MAX
#define UINT_FAST64_MAX UINT64_MAX
/* 7.18.2.4 Limits of integer types capable of holding object pointers */
#if __WORDSIZE == 64
#define INTPTR_MIN INT64_MIN
#define INTPTR_MAX INT64_MAX
#else
#define INTPTR_MIN INT32_MIN
#define INTPTR_MAX INT32_MAX
#endif
#if __WORDSIZE == 64
#define UINTPTR_MAX UINT64_MAX
#else
#define UINTPTR_MAX UINT32_MAX
#endif
/* 7.18.2.5 Limits of greatest-width integer types */
#define INTMAX_MIN INT64_MIN
#define INTMAX_MAX INT64_MAX
#define UINTMAX_MAX UINT64_MAX
/* 7.18.3 "Other" */
#if __WORDSIZE == 64
#define PTRDIFF_MIN INT64_MIN
#define PTRDIFF_MAX INT64_MAX
#else
#define PTRDIFF_MIN INT32_MIN
#define PTRDIFF_MAX INT32_MAX
#endif
#if __WORDSIZE == 64
#define SIZE_MAX UINT64_MAX
#else
#define SIZE_MAX UINT32_MAX
#endif
#if defined(__STDC_WANT_LIB_EXT1__) && __STDC_WANT_LIB_EXT1__ >= 1
#define RSIZE_MAX (SIZE_MAX >> 1)
#endif
#ifndef WCHAR_MAX
# ifdef __WCHAR_MAX__
# define WCHAR_MAX __WCHAR_MAX__
# else
# define WCHAR_MAX 0x7fffffff
# endif
#endif
/* WCHAR_MIN should be 0 if wchar_t is an unsigned type and
(-WCHAR_MAX-1) if wchar_t is a signed type. Unfortunately,
it turns out that -fshort-wchar changes the signedness of
the type. */
#ifndef WCHAR_MIN
# if WCHAR_MAX == 0xffff
# define WCHAR_MIN 0
# else
# define WCHAR_MIN (-WCHAR_MAX-1)
# endif
#endif
#define WINT_MIN INT32_MIN
#define WINT_MAX INT32_MAX
#define SIG_ATOMIC_MIN INT32_MIN
#define SIG_ATOMIC_MAX INT32_MAX
/* 7.18.4 Macros for integer constants */
#define INT8_C(v) (v)
#define INT16_C(v) (v)
#define INT32_C(v) (v)
#define INT64_C(v) (v ## LL)
#define UINT8_C(v) (v ## U)
#define UINT16_C(v) (v ## U)
#define UINT32_C(v) (v ## U)
#define UINT64_C(v) (v ## ULL)
#ifdef __LP64__
#define INTMAX_C(v) (v ## L)
#define UINTMAX_C(v) (v ## UL)
#else
#define INTMAX_C(v) (v ## LL)
#define UINTMAX_C(v) (v ## ULL)
#endif
#endif /* _STDINT_H_ */