各位可以试试，结果保障大吃一惊：
void main(void)
{
    unsigned int a = 0xFFFFFF80;
    unsigned int b = 0xFFFFFF7f;
    char *pa = (char *)&a;
    char *pb = (char *)&b;
    printf("%08x,%08x\n",*pa,*pb);
}