C语言 位域:十进制数字与二进制数字的相互转换

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
typedef struct
{
	char b1:1;
	char b2:1;
	char b3:1;
	char b4:1;
	char b5:1;
	char b6:1;
	char b7:1;
	char b8:1;
}bit_t;

typedef union
{
	int dnum;
	char cnum[4];
}char_t;

char* CharToBinary(char num)
{
	bit_t *bit;
	bit=(bit_t*)&num;
	
	char strnum[17]={0};
	sprintf(strnum,"%d%d%d%d%d%d%d%d\n",
			bit->b8,bit->b7,bit->b6,bit->b5,
			bit->b4,bit->b3,bit->b2,bit->b1);
	
	char *bnum=(char*)malloc(10);
	for(int j=0,i=0;i<17;i++)
	{
		if(strnum[i]==0)
			break;
		if(strnum[i]!='-')
			bnum[j++]=strnum[i];
		if(j==4)
			bnum[j++]=' ';
	}
	bnum[9]=' ';
	return bnum;
}

int BinaryToInt(char *s)
{	
	char_t num;
	int len=strlen(s)-1;
	for(int i=len/8;i>=0;i--)
	{
		bit_t *bit;
		bit=(bit_t*)&num.cnum[i];
		int index=len-i*8;		
		
		bit->b1=index<0?0:(s[index--]-'0'==0?0:1);
		bit->b2=index<0?0:(s[index--]-'0'==0?0:1);
		bit->b3=index<0?0:(s[index--]-'0'==0?0:1);
		bit->b4=index<0?0:(s[index--]-'0'==0?0:1);
		bit->b5=index<0?0:(s[index--]-'0'==0?0:1);
		bit->b6=index<0?0:(s[index--]-'0'==0?0:1);
		bit->b7=index<0?0:(s[index--]-'0'==0?0:1);
		bit->b8=index<0?0:(s[index--]-'0'==0?0:1);
	}

	return num.dnum;	
}

int main(int argc,char**argv)
{
	if(argc!=3)
	{
		puts("请输入参数 \n\t-b\t十进制转换为二进制\n\t-d\t二进制转换为10进制"); 
	return 0;
	}
	
	if(!strcmp(argv[1],"-b"))
	{
		char_t num;
		num.dnum=atoi(argv[2]);
		printf("十进制为 %d\n二进制为 ",num.dnum);
		char ret[33]={0};
		char flag=0;
		for(int i=3;i>=0;i--)
			if(num.cnum[i]!=0||flag)
			{
				flag=1;				//防止256之类的数字跳过
				char *p=CharToBinary(num.cnum[i]);
				printf("%s",p);
		 		free(p);
			}

		puts("");
		return 0;
	}
	else if(!strcmp(argv[1],"-d"))
	{
		printf("二进制为 %s\n十进制为 %d\n",argv[2],BinaryToInt(argv[2]));
		return 0;
	}
	else
		puts("参数错误,输入程序名可查看帮助");

	return 0;
}