2.60 替换指定字节数据

//csapp 2.60 

#include <stdio.h>                                                                                                                         
#include <inttypes.h>

typedef unsigned char * char_point;

uint32_t replace_byte(uint32_t x, int i, unsigned char b)
{
    if(i > 3 || i < 0) {
        return -1;
    }

    char_point char_date_point = ((char_point) &x) + i;

    *char_date_point = b;

    printf("result : %X\r\n", x);
    return x;
}

int main(void)
{
    unsigned char replace_data = 0xAB;

    uint32_t x = 0x12345678;
    uint32_t  r_x = 0x12AB5678;
    int i_x = 2;


    uint32_t  y = x;
    uint32_t r_y = 0x123456AB;
    int i_y = 0;

    printf("r_x == result : %d\r\n", r_x == replace_byte(x, i_x, replace_data));
    printf("r_y == result : %d\r\n", r_y == replace_byte(y, i_y, replace_data));

    return 1;
}