两个字符转为一个字符

'a', 'b'
=>
0xab (16进制表示)

#include <stdio.h>
#include <string.h>
#include <ctype.h>

unsigned char char2Hex(unsigned char left,
                       unsigned char right)
{
    const char *hex = "0123456789ABCDEF";
    int l = strchr(hex, toupper(left)) - hex;
    int r = strchr(hex, toupper(right)) - hex;

    return l * 16 + r;
}

int main(int argc, char *argv[])
{
    printf("%x\n", char2Hex('a', 'b'));
    // output: ab
    return 0;
}