判断字节顺序的小程序

时间：2010-09-13 来源：litan1986

网络编程中，字节顺序是个很重要的东东，搞不明白，在异构计算机之间通信很容易出问题。所谓字节顺就是某种数据类型内部字节的顺序，学习过x86汇编应该都知道这么一点，“低位存储在低字节，高位存储在高字节”，这就是所谓的little_endian,相反的叫big_endian,但是要注意的是不要把所有的机器都想象成x86体系结构的little_endian存储，要考虑到程序的通用性和可移植性。下面一段小代码可以判断机器的字节顺序

#include<stdio.h>
#define is_little_endian3(x) *(char *)&x
union endian_un
{
    short var;
    char bits[sizeof(short)];
};
int is_little_endian1()
{
    union endian_un flag;
    flag.var=0x0102;
    if(flag.bits[0]==1&&flag.bits[1]==2)
        return 0;
    else
        return 1;
}
int is_little_endian2()
{
    unsigned short flag=0x4321;
    if(*(char *)&flag==0x21)
        return 1;
    else
        return 0;
}

int main()
{

    if(is_little_endian1())
        printf("judge by method 1,little-endian\n");
    else
        printf("judge by method 1,big-endian\n");

    if(is_little_endian2())
        printf("judge by method 2,little-endian\n");
    else
        printf("judge by method 2,big-endian\n");

    short a=0x00ff;
    if(is_little_endian3(a))
        printf("judge by method 3,little-endian\n");
    else
        printf("judge by method 3,big-endian\n");

    return 0;
}