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utils.h

#ifndef UTILS_H
#define UTILS_H

int Hex2Char(int fromi,char *toc);
int Char2Hex(char fromc,int *toi);
int BitStr2ByteArr(char *bs,char *ba);
int ByteArr2BitStr(char *ba,char *bs);
int INT2ByteArr(int i,char *ba);
int ByteArr2INT(char *ba,int *i);

#endif

utils.c

#include<stdio.h>
#include<utils.h>
#include<string.h>
int Hex2Char(int fromi,char *toc)
{
    if(fromi>=0&&fromi<=9){
        *toc= fromi+'0';
    } 
    else if(fromi>=10&&fromi<=15){
        *toc = fromi+'A'-10;
    }
    else{
        printf("error!");
     }
    return 0;}
int Char2Hex(char fromc,int *toi)
{
    if(fromc>='0'&& fromc<='9')
    {
             *toi= fromc-'0';
    }
    else if(fromc>='A'&& fromc<='F')
    {
             *toi= fromc-'A'+10;
        }
        else {
            printf("error!");
        }
    return 0;}

int ByteArr2BitStr(char *ba,char *bs)
{
    int i,j,l;
    int len;
    len = strlen(ba);
    for(j=0;j<len;j++)
    {
        Char2Hex(ba[j],&l);
        for(i=0;i<4;i++)//4位 
        {
            
            bs[3*(j+1)-i+j] = l%2+'0';
            l=l/2;
        }
    }
    bs[4*len]='\0';
}
int BitStr2ByteArr(char *bs,char *ba){
   int len;
   len = strlen(bs);
   char string[100];int i,j,c;int sum=0;
   if(len%4==1)
   {
     strcpy(string,"000");
     strcat(string,bs);
     c=len/4+1;

   }
   else if(len%4==2)
   {
     strcpy(string,"00");
     strcat(string,bs);
     c=len/4+1;
   }
    else if(len%4==3)
   { 
      strcpy(string,"0");;
      strcat(string,bs);
      c=len/4+1;
   }
   else
   {
       c=len/4;
       strcpy(string,bs);
   }
   for(i=0;i<c;i++)
   { for(j=0;j<4;j++)
       { 
           sum=sum*2;
           sum=sum+(string[4*i+j]-'0'); 
       }
       Hex2Char(sum,&ba[i]);
       sum=0;   }
   ba[i]='\0';

}

main.c

#include<stdio.h>
#include<utils.h>
int main(){
  char bytestr[100];
  char  bitsstr[100];
  printf("输入一串字节串");
  scanf("%s",bytestr);
  ByteArr2BitStr(bytestr,bitsstr);
  printf("计算出的位串为\n");
  printf("%s\n",bitsstr);

  char bytestr_1[100];
  char  bitsstr_1[100];
  printf("请输入一串位串:");
  scanf("%s",bitsstr_1);
  printf("将位串转化为字节数组\n");
  BitStr2ByteArr(bitsstr_1,bytestr_1);
  printf("打印出字节数组:\n");
  printf("%s\n",bytestr_1);
  return 0;
}

运行结果