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; 
}