详解dll动态库的开发与调用及文件的读写小程序

#include <stdio.h> #include <stdlib.h> /*   该代码是对文件读写操作的使用 */ #pragma warning(disable:4996) #define MAX_DATA_LEN 4096 //进行加密的函数 int FileSymEnc(char * from, char * to);  void main() {    char * from = "C:/Users/Administrator/Desktop/结构体的拷贝问题.docx";   char * to = "C:/Users/Administrator/Desktop/副本结构体的拷贝问题.docx";   //下面调用函数进行文件的读写   int re = FileSymEnc(from, to);   if (re == 0) {     printf("文件读写错误！");   }   system("pause"); }  int FileSymEnc(char * from, char * to) {   //返回值，以确定执行状态,-0代表失败,1代表成功   int re = 1;   //写了几个   int writtenLen = 0;   //准备写几个   int plainlen = 0;   //在堆区分配4k内存空间   unsigned char * buff = malloc(MAX_DATA_LEN);   buff = memset(buff, 0, MAX_DATA_LEN);   FILE * f = fopen(from, "rb");   FILE * t = fopen(to, "wb");   if (f == NULL) {     printf("打开读文件错误！");     goto END;   }   if (t == NULL) {     printf("打开写文件错误！");     goto END;   }    while (!feof(f))   {      writtenLen = fread(buff, 1, MAX_DATA_LEN, f);     //判读是否读到了文件末尾，如果读到了则跳出循环     if (feof(f))     {       plainlen = writtenLen;       break;     }      if (writtenLen != MAX_DATA_LEN) {       //没有读取成功       printf("文件读入失败！");       re = 0;       goto END;     }     //读取成功进行文件的写入     writtenLen = fwrite(buff, 1, MAX_DATA_LEN, t);     if (writtenLen != MAX_DATA_LEN) {       printf("文件写入失败！");       re = 0;       goto END;     }   }    //外面处理不到4K的写入问题，我们本不用进行格外的小数据读写，主不过这和我们的加密方式相关连得   writtenLen = fwrite(buff, 1, plainlen, t);   if (writtenLen != plainlen) {     printf("文件写入失败！");     re = 0;     goto END;   }  END:   //堆分配的内存进行释放   if (buff != NULL) {     free(buff);     buff = NULL;   }   //进行文件的关闭操作    if (f != NULL) {     fclose(f);     f = NULL;   }   if (t != NULL) {     fclose(t);     f = NULL;   }   return re; }