c - 在C中用位操作打包和解包数据

Question

我尝试用 C 中的位操作对数据进行打包和解包。我的期望是，如果我输入 4 个输入 1、2、3、4，那么输出应该是 1234。但我没有得到预期的输出。请让我知道我的代码有什么问题，或者我预期的输出本身就是错误的。

#include <stdio.h>

void displabits(int input)
{
    int mask=0x1, i;
    for (i=31; i>=0; i--)
    {
        mask = 1 << i;
        putchar((input & mask)? '1' : '0');
       if(i%8 == 0)
           putchar(' ');
    }
    printf("\n");
}

int main()
{
    int a, b, c, d, packed_output=0, mask=0x1, p=0, q=0, r=0, s=0, temp;
    printf("Enter first character\r\n");
    scanf("%d",&a);
    displabits(a);
    printf("Enter second character\r\n");
    scanf("%d",&b);
    displabits(b);
    printf("Enter third character\r\n");
    scanf("%d",&c);
    displabits(c);
    printf("Enter fourth character\r\n");
    scanf("%d",&d);
    displabits(d);
    a = a << 24;
    displabits(a);
    b = b << 16;
    displabits(b);
    c = c << 8;
    displabits(c);
    /* Packing data start */
    packed_output = packed_output | a;
    packed_output = packed_output | b;
    packed_output = packed_output | c;
    packed_output = packed_output | d;
    printf("packed_output = %d\r\n", packed_output);
    printf("packed_output in 32 bit format formar");
    displabits(packed_output);
    /* Packing data end */

    /* Unpacking data start */
    mask = ~(~0<<8)<<(31-8+1);
    p = packed_output & mask;
    p = p >> 24;
    mask = ~(~0<<8)<<(23-8+1);
    q = packed_output & mask;
    q = q >> 16;
    mask = ~(~0<<8)<<(15-8+1);
    r = packed_output & mask;
    r = r >> 8;
    mask = ~(~0<<8)<<(7-8+1);
    s = packed_output & mask;
    printf("unpacked output's are as follows\r\n");
    printf("first character = %d\r\n", p);
    printf("first character in bit format\r\n");
    displabits(p);
    printf("second character = %d\r\n", q);
    printf("second character in bit format\r\n");
    displabits(q);
    printf("third character = %d\r\n", r);
    printf("third character in bit format\r\n");
    displabits(r);
    printf("fourth character = %d\r\n", s);
    printf("fourth character in bit format\r\n");
    displabits(s);
    /* Unpacking data end */    
    return 0;
}

我已将打包和解包逻辑放在同一个代码库中。

Answer 1

主要问题是你在不同的基地进行操作。这就是为什么你会得到意想不到的答案。 n << p是二进制运算，实际上等于n * (2 ^ p) .然而，你想要的是 n * (10 ^ r) .所以，如果你想以人类可读的形式得到你的答案，你需要一个常规的十进制算法，比如:

a = a * 1000;
b = b * 100;
c = c * 10;
packed_output += a;
packed_output += b;
packed_output += c;
packed_output += d;