c - 如何在 C 函数中像 unsigned 那样生成有符号字符

Question

我正在尝试在 C 中编码字符，替换奇数位索引之间的偶数索引位，如下所示

 'W' = 57h = 0101_0111
       ABh = 1010_1011

并且因为 C 中的 char 可能会变成负数，所以我无法在位之间切换(仅在 signed char 中 - 它有效)。它给了我另一种值(value)在下面的代码中。

#include <stdio.h>
#include <limits.h>
#define TRUE 1
#define ONE 1

char codeBinPair(char str);

void main()
{
char str[2] = { 182,NULL };
unsigned char ch = 'W';
printf("ch = %x\n", ch);
ch = codeBinPair(ch);
printf("ch = %x\n", ch);
ch = codeBinPair(ch);
printf("ch = %x\n", ch);
}

char codeBinPair(char str)
{
    int idx = 0;
    char ch1 = str, ch2 = 0, mask = ONE;
    while (TRUE) 
    {
    mask <<= ONE;
    mask &= ch1;
    mask >>= ONE;
    ch2 |= mask;
    // Initialize the mask
    mask = ONE;
    mask <<= idx;
    mask &= ch1;
    mask <<= ONE;
    ch2 |= mask;
     // Index next loop we want to replace
     idx += 2;
     // If We Finish whole Byte
     if (idx == CHAR_BIT)
        return ch2;
     // Initialize the mask
     mask = ONE;    
     mask <<= idx;
 }
}

Answer 1

将codeBinPair中的所有char更改为unsigned char。

unsigned char codeBinPair(unsigned char str)
{
    int idx = 0;
    unsigned char ch1 = str, ch2 = 0, mask = ONE;
    while (TRUE) 
        {
            mask <<= ONE;
            mask &= ch1;
            mask >>= ONE;
            ch2 |= mask;
            // Initialize the mask
            mask = ONE;
            mask <<= idx;
            mask &= ch1;
            mask <<= ONE;
            ch2 |= mask;
            // Index next loop we want to replace
            idx += 2;
            // If we finish whole byte
            if (idx == CHAR_BIT)
                return ch2;
            // Initialize the mask
            mask = ONE;    
            mask <<= idx;
        }
}