CS:APP解题记录

CS:APP 2.60

#include <stdio.h>
unsigned replace_byte(unsigned x, int i, unsigned char b)
{
    x = x & (~(0XFF << (i << 3)));//相应字节置零
    x = x | (b << (i << 3));      //相应字节改为char b
    return x;
}
int main()
{
    unsigned ret = replace_byte(0X12345678, 1, 0XAB);
    printf("0X%X\n", ret);
    return 0;
}

0X1234AB78

利用按位运算$x \& 1 = x , b | 0 = b$。