?

//輸出格式: 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 != '/0'; ++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 = '/0';
?? return ptr;
}