复制代码 代码如下:

//======================================

//输出格式: hex2bin 5e.

//得到: 0101 1110

//======================================

#include <stdio.h>

#include <limits.h>

char *bitstr(char *, void const *, size_t);

int main(int argc, char **argv)

{

unsigned char value;

char *pointer;

char ebits[CHAR_BIT * sizeof value + 1];

value = 0;

for (pointer = argv[1]; *pointer; ++pointer) {

value <<= 4;

switch (*pointer) {

case 'a':

case 'A':

value += 0xa;

break;

case 'b':

case 'B':

value += 0xb;

break;

case 'c':

case 'C':

value += 0xc;

break;

case 'd':

case 'D':

value += 0xd;

break;

case 'e':

case 'E':

value += 0xe;

break;

case 'f':

case 'F':

value += 0xf;

break;

default:

value += *pointer - '0';

break;

}

}

bitstr(ebits, &value, sizeof value);

printf("The binary representation of 0x%s is ", argv[1]);

for (pointer = ebits, value = 0; *pointer != ''; ++pointer) {

if(value > 3) {

value = 0;

putchar(' ');

putchar(*pointer);

}

else {

value++;

putchar(*pointer);

}

}

return 0;

}

char *bitstr(char *str, const void *obj, size_t n)

{

unsigned char mask;

const unsigned char *byte = obj;

char *const ptr = str;

while (n--) {

mask = ((unsigned char)-1 >> 1) + 1;

do {

*str++ = (char)(mask & byte[n] ? '1' : '0');

mask >>= 1;

} while (mask);

}

*str = '';

return ptr;

}