c语言实现把‘0’和‘1’字符串转化为二进制压缩保存成二进制文件

/*
功能：
writeBit(char *ch)把'0'和'1'组成的字符串，压缩存储二进制在bit.txt文件
bit.txt文件结构如下：开头4个字节保存了该文件存储的位数，后面的字节为存储内容

readBit()把二进制文件bit.txt恢复成字符串。
*/

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

void writeBit(char *ch);
void readBit();
int main()
{
char ch[500];

scanf("%s", ch);

writeBit(ch);

readBit();

return 0;
}

void writeBit(char *ch)
{
int i;
int j;
char dest;
int count = 0; //计算字符串个数
int  num;    //存储字符需要的多少个字节
int left;	//字符串剩余不足8位的个数
FILE *fp = NULL;
char *p = NULL;

if (NULL == (fp = fopen("bit.txt", "wb")))
{
printf("open file error\n");
}

for (i = 0; ch[i] != 0; i++)
{
count++;        //统计字符个数
}
num = count / 8;
left = count % 8;
printf("\n字符串共有字符%d个，占%d字节\n存储成bit.txt文件后，占%d字节\n", count, count,
(left != 0?4+num + 1 : 4+num));

if (left == 0)	//如果left为0，那么num个字节刚好能够存放，否则需要num + 1字节
{
p = (char *)malloc(sizeof(char) * num);
memset(p, 0, num);
}
else
{
p = (char *)malloc(sizeof(char) * (num + 1));
memset(p, 0, num + 1);
}

j = -1;
for (i = 0; i < count; i++)//位运算，每8个字符以2进制的形式储存在一个字符中
{
if (i % 8 == 0)
{
j++;
}
p[j] <<= 1;
ch[i] -= '0';
p[j] |= ch[i];
}

if (left != 0) //如果left不为0，需要把剩余的几个位向左边靠拢
{
p[j] <<= 8 - left; //例如left为2，即00000011，需要左移6位变为11000000
fwrite(&count, sizeof(count), 1, fp);
fwrite(p, 1, num + 1 , fp);

}
else
{
fwrite(&count, sizeof(count), 1, fp);
fwrite(p, 1, num , fp);

}

fclose(fp);

}

void readBit()
{
FILE *fp = NULL;
int count;
int num;
int left;
int i, j;
unsigned char flag = 128;	//即0b1000000,用于做位运算 ,注意要用无符号的字符型
char *p = NULL;

if (NULL == (fp = fopen("bit.txt", "rb")))
{
printf("open file error\n");
}

fread(&count, sizeof(count), 1, fp);
num = count / 8;
left = count % 8;

if (left == 0)
{
p = (char *)malloc(sizeof(char) * num);
fread(p, 1, num, fp);
}
else
{
p = (char *)malloc(sizeof(char) * (num + 1));
fread(p, 1, num + 1, fp);
}
fclose(fp);

j = -1;
printf("\nbit.txt文件存储的二进制为:\n");
for (i = 0; i < count; i++)
{
if (i % 8 == 0)
{
j++;
flag = 128;
}

if ((p[j] & flag))//通过改变flag字符2进制1的位置判读，一个字节哪个位是1，哪个位是0
{						//并输出字符形式
printf("1");
flag /= 2;
}
else
{
printf("0");
flag /= 2;
}

}
printf("\n");
}