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原文地址： http://www.milkcu.com/blog/archives/1367305920.html
前言
聲明一個(gè)變量，經(jīng)常要考慮的問(wèn)題是這個(gè)類(lèi)型的變量能不能裝的下。今天 MilkCu 就總結(jié)下吧，以解除后顧之憂。
關(guān)于變量取值范圍的問(wèn)題，在Kernighan的《C程序設(shè)計(jì)語(yǔ)言》第28頁(yè)練習(xí)2-1就提到過(guò)。
編寫(xiě)一個(gè)程序以確定分別由signed及unsigned限定的char、short、int與long類(lèi)型變量的取值范圍。采用打印標(biāo)準(zhǔn)頭文件中的相應(yīng)值以及直接計(jì)算兩種方式實(shí)現(xiàn)。后一種方式的實(shí)現(xiàn)較困難一些，因?yàn)橐_定各種浮點(diǎn)類(lèi)型的取值范圍。
這書(shū)是針對(duì)C89的，隨著C99及C++的廣泛應(yīng)用long long int類(lèi)型也是一種美妙的選擇。
實(shí)現(xiàn)方案
標(biāo)準(zhǔn)規(guī)定：各種類(lèi)型的取值范圍必須在頭文件<limits.h>中定義。不同類(lèi)型在不同的硬件上有不同的長(zhǎng)度，所以它們?cè)诓煌瑱C(jī)器上的取值范圍也往往會(huì)不同。我們可以通過(guò)頭文件確定類(lèi)型取值范圍。
函數(shù)sizeof()
可以通過(guò)函數(shù)sizeof()用字節(jié)計(jì)算參數(shù)并返回的字節(jié)數(shù)，間接得到類(lèi)型寬度，源代碼如下：
# include <stdio.h>
int main(void)
{
printf("byte of short = %d\n", sizeof(short));
printf("byte of int = %d\n", sizeof(int));
printf("byte of long = %d\n", sizeof(long));
printf("byte of long long int = %d\n", sizeof(long long int));
return 0;
}
打印常量
可以通過(guò)打印頭文件的方法獲得每種類(lèi)型的取值范圍：
# include <stdio.h>
# include <limits.h>
//determine ranges of types
int main(void)
{
//signed types
printf("signed char min = %d\n", SCHAR_MIN);
printf("signed char max = %d\n", SCHAR_MAX);
printf("signed short min = %d\n", SHRT_MIN);
printf("signed short max = %d\n", SHRT_MIN);
printf("signed short min = %d\n", INT_MIN);
printf("signed long min = %ld\n", LONG_MIN);
printf("signed long max = %ld\n", LONG_MAX);
printf("signed long long int min = %lld\n", LONG_LONG_MIN);
printf("signed long long int max = %lld\n", LONG_LONG_MAX);
//unsigned types
printf("unsigned char max = %u\n", UCHAR_MAX);
printf("unsigned short max = %u\n", USHRT_MAX);
printf("unsigned int max = %u\n", UINT_MAX);
printf("unsigned long max = %lu\n", ULONG_MAX);
printf("unsigned long long int max = %llu\n", ULONG_LONG_MAX);
return 0;
}
打印結(jié)果如下：
signed char min = -128
signed char max = 127
signed short min = -32768
signed short max = -32768
signed short min = -2147483648
signed long min = -2147483648
signed long max = 2147483647
signed long long int min = -9223372036854775808
signed long long int max = 9223372036854775807
unsigned char max = 255
unsigned short max = 65535
unsigned int max = 4294967295
unsigned long max = 4294967295
unsigned long long int max = 18446744073709551615
頭文件
可以從頭文件<limits.h>中更詳細(xì)的看到它們的宏定義，<limits.h>（來(lái)自 Dev-Cpp 5.4.0 MinGW 4.7.2 ）如下：
/*
* limits.h
* This file has no copyright assigned and is placed in the Public Domain.
* This file is a part of the mingw-runtime package.
* No warranty is given; refer to the file DISCLAIMER within the package.
*
* Functions for manipulating paths and directories (included from io.h)
* plus functions for setting the current drive.
*
* Defines constants for the sizes of integral types.
*
* NOTE: GCC should supply a version of this header and it should be safe to
* use that version instead of this one (maybe safer).
*
*/
#ifndef _LIMITS_H_
#define _LIMITS_H_
/* All the headers include this file. */
#include <_mingw.h>
/*
* File system limits
*
* TODO: NAME_MAX and OPEN_MAX are file system limits or not? Are they the
* same as FILENAME_MAX and FOPEN_MAX from stdio.h?
* NOTE: PATH_MAX is the POSIX equivalent for Microsoft's MAX_PATH; the two
* are semantically identical, with a limit of 259 characters for the
* path name, plus one for a terminating NUL, for a total of 260.
*/
#define PATH_MAX 260
/*
* Characteristics of the char data type.
*
* TODO: Is MB_LEN_MAX correct?
*/
#define CHAR_BIT 8
#define MB_LEN_MAX 2
#define SCHAR_MIN (-128)
#define SCHAR_MAX 127
#define UCHAR_MAX 255
/* TODO: Is this safe? I think it might just be testing the preprocessor,
* not the compiler itself... */
#if ('\x80' < 0)
#define CHAR_MIN SCHAR_MIN
#define CHAR_MAX SCHAR_MAX
#else
#define CHAR_MIN 0
#define CHAR_MAX UCHAR_MAX
#endif
/*
* Maximum and minimum values for ints.
*/
#define INT_MAX 2147483647
#define INT_MIN (-INT_MAX-1)
#define UINT_MAX 0xffffffff
/*
* Maximum and minimum values for shorts.
*/
#define SHRT_MAX 32767
#define SHRT_MIN (-SHRT_MAX-1)
#define USHRT_MAX 0xffff
/*
* Maximum and minimum values for longs and unsigned longs.
*
* TODO: This is not correct for Alphas, which have 64 bit longs.
*/
#define LONG_MAX 2147483647L
#define LONG_MIN (-LONG_MAX-1)
#define ULONG_MAX 0xffffffffUL
#ifndef __STRICT_ANSI__
/* POSIX wants this. */
#define SSIZE_MAX LONG_MAX
#endif
#if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L) \
|| !defined(__STRICT_ANSI__)
/* ISO C9x macro names */
#define LLONG_MAX 9223372036854775807LL
#define LLONG_MIN (-LLONG_MAX - 1)
#define ULLONG_MAX (2ULL * LLONG_MAX + 1)
#endif
/*
* The GNU C compiler also allows 'long long int'
*/
#if !defined(__STRICT_ANSI__) && defined(__GNUC__)
#define LONG_LONG_MAX 9223372036854775807LL
#define LONG_LONG_MIN (-LONG_LONG_MAX-1)
#define ULONG_LONG_MAX (2ULL * LONG_LONG_MAX + 1)
/* MSVC compatibility */
#define _I64_MIN LONG_LONG_MIN
#define _I64_MAX LONG_LONG_MAX
#define _UI64_MAX ULONG_LONG_MAX
#endif /* Not Strict ANSI and GNU C compiler */
#endif /* not _LIMITS_H_ */
閱讀頭文件，在注釋的幫助下，我們可以更明確的看到數(shù)據(jù)類(lèi)型的定義。
總結(jié)
簡(jiǎn)而言之，對(duì)于MinGW32：
int類(lèi)型，能完整表示9位；
unsigned long long int類(lèi)型，能完整表示19位。
后記
又一輪新生活開(kāi)始了，要充實(shí)快樂(lè)每一天。
借用奧斯托洛夫斯基在 《鋼鐵是怎樣煉成》 中的幾句話吧：
人最寶貴的東西是生命
生命屬于人只有一次
一個(gè)人的生命是應(yīng)該這樣度過(guò)的
當(dāng)他回首往事的時(shí)候
他不會(huì)因虛度年華而悔恨
也不會(huì)因碌碌無(wú)為而羞恥
這樣在臨死的時(shí)候
他才能夠說(shuō)：“我的生命和全部的經(jīng)歷
都獻(xiàn)給世界上最壯麗的事業(yè)——為人類(lèi)的解放而斗爭(zhēng)”。
（全文完）
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