字节存放顺序：大尾，小尾

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    short int a = 0x1234;
    char *p = (char *)&a;

    printf("p=%#hhx\n", *p);

    if (*p == 0x34) {
        printf("little endian\n");   
    } else if (*p == 0x12) {
        printf("big endia\n");   
    } else {
        printf("unknown endia\n");   
    }
    return 0;
}

#define sw16(x) \
    ((short)( \
        (((short)(x) & (short)0x00ffU) << 8 ) | \
        (((short)(x) & (short)0xff00U) >> 8 ) ))