文件操作（二进制文件加密解密）

加密

#include<stdio.h>
#include<string.h>void code(char *p,size_t n)
{size_t i;for(i = 0; i < n; i++){p[i] += 3;}
}int main()
{FILE *p1 = fopen("./a.txt","r");FILE *p2 = fopen("./b.txt","w");char buf[1024] = {0};while(!feof(p1)){memset(buf,0,sizeof(buf));size_t res = fread(buf,sizeof(char),sizeof(buf),p1);code(buf,res);fwrite(buf,sizeof(char),res,p2);}fclose(p1);fclose(p2);return 0;
}

解密：

/***
decode.c
***/
#include<stdio.h>
#include<string.h>void decode(char *p,size_t n)
{size_t i;for(i = 0; i < n; i++){p[i] -= 3;}
}int main()
{FILE *p1 = fopen("./b.txt","rb");FILE *p2 = fopen("./c.txt","wb");char buf[1024] = {0};while(!feof(p1)){memset(buf,0,sizeof(buf));size_t res = fread(buf,sizeof(char),sizeof(buf),p1);decode(buf,res);fwrite(buf,sizeof(char),res,p2);}fclose(p1);fclose(p2);return 0;
}