在 C 中显示数字的二进制表示? [英] Display the binary representation of a number in C?

问题描述

可能重复:
是否有 printf 转换器可以以二进制格式打印?

还在学习C，我想知道:

Still learning C and I was wondering:

给定一个数字，是否可以执行以下操作?

Given a number, is it possible to do something like the following?

char a = 5;
printf("binary representation of a = %b",a);
> 101

或者我是否必须编写自己的方法来进行二进制转换?

Or would i have to write my own method to do the transformation to binary?

推荐答案

是的(自己写)，类似下面的完整函数.

Yes (write your own), something like the following complete function.

#include <stdio.h> /* only needed for the printf() in main(). */
#include <string.h>

/* Create a string of binary digits based on the input value.
   Input:
       val:  value to convert.
       buff: buffer to write to must be >= sz+1 chars.
       sz:   size of buffer.
   Returns address of string or NULL if not enough space provided.
*/
static char *binrep (unsigned int val, char *buff, int sz) {
    char *pbuff = buff;

    /* Must be able to store one character at least. */
    if (sz < 1) return NULL;

    /* Special case for zero to ensure some output. */
    if (val == 0) {
        *pbuff++ = '0';
        *pbuff = '';
        return buff;
    }

    /* Work from the end of the buffer back. */
    pbuff += sz;
    *pbuff-- = '';

    /* For each bit (going backwards) store character. */
    while (val != 0) {
        if (sz-- == 0) return NULL;
        *pbuff-- = ((val & 1) == 1) ? '1' : '0';

        /* Get next bit. */
        val >>= 1;
    }
    return pbuff+1;
}

将此 main 添加到它的末尾以查看它的运行情况:

Add this main to the end of it to see it in operation:

#define SZ 32
int main(int argc, char *argv[]) {
    int i;
    int n;
    char buff[SZ+1];

    /* Process all arguments, outputting their binary. */
    for (i = 1; i < argc; i++) {
        n = atoi (argv[i]);
        printf("[%3d] %9d -> %s (from '%s')
", i, n,
            binrep(n,buff,SZ), argv[i]);
    }

    return 0;
}

用 "progname 0 7 12 52 123" 运行得到:

[  1]         0 -> 0 (from '0')
[  2]         7 -> 111 (from '7')
[  3]        12 -> 1100 (from '12')
[  4]        52 -> 110100 (from '52')
[  5]       123 -> 1111011 (from '123')

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