C/C++详解如何实现文件备份

#include<bits/stdc++.h>
#define ios ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
using namespace std;
signed main(void){ios; //c ++ 的关流, 不用管
  FILE *fp, *fq; //建立文件的索引指针
  if((fp = fopen("source" , "ra"))){ //打开需备份文件, 并且得到文件索引指针头
    cout << "success in readfile open!" << endl;
  }else{
    cout << "can\'t open readfile!" << endl;
    exit(1);
  }
  if((fq = fopen("target" , "wa"))){ //建立(打开)目标文件, 并且得到文件索引指针头
    cout << "success in writefile open!" << endl;
  }else {
    cout << "can\'t open writefile!" << endl;
    exit(1);
  }
  char buffer[20]; //设置一个缓冲区.
  while(fread(buffer, sizeof(char), 20, fp)){ //在需备份中一直获取内容
    fwrite(buffer, sizeof(char), 20, fq); //获取内容后一直同步输入目标文件
  }
  if(!fclose(fp)){ //关闭成功的返回值为0
    cout << "success in readfile close!" << endl;
  }else {
    cout << "can\'t close readfile!" << endl;
    exit(1);
  }
  if(!fclose(fq)){
    cout << "success in writefile close!" << endl;
  }else {
    cout << "can\'t close writefile!" << endl;
    exit(1);
  }
  return 0;
}

#include<bits/stdc++.h>
#define ios ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
using namespace std;
signed main(void){ios; //c ++ 的关流, 不用管
  freopen("source" , "r" , stdin);
  freopen("target" , "w" , stdout);
  char c;
  while((c = getchar()) != EOF) putchar(c);
  return 0;
}

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
signed main(int argc, char **argv) {
    int fp, fq;  //源文件的文件描述符, 目标文件的文件描述符
    char buffer[20];
    int nread;
    //判断参数个数是否正确
    if (argc != 3) {
        printf("error~");
        exit(1);
    }
    //打开源文件
    if ((fp = open(argv[1], O_RDONLY)) == -1) {
        printf("Open readfile Erron\n");
        exit(1);
    }
    //创建目标文件
    if ((fq = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR)) == -1) {
        printf("Open writefile Error\n");
        exit(1);
    }
    //进行文件拷贝
    while ((nread = read(fp, buffer, 20)) > 0) {
        if ((write(fq, buffer, nread)) != nread)  //将buffer中的数据写到目的文件
            printf("write error");
    }
    close(fp);
    close(fq);
    return 0;
}