使用ifstream、ofstream和fstream [英] Using ifstream, ofstream and fstream

问题描述

1. 正在尝试将"beave"一词读入文件

2. 稍后将文件内容编辑为用户想要的内容，并将其存储在字符串"line"中

3. 文件从不显示，当我手动检查时，文本文件为空。

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    string line = { " " };
    ofstream file1;
    file1.open("beef.txt");
    file1 << "beef" << endl;
    file1.close();
    file1.open("beef.txt");

    if (file1.is_open())
    {
        cout << "Enter what you would like to be contained in the file" << endl;
        cin >> line;
        ofstream file1;
        file1 << line << endl;
    }

    return 0;
}

推荐答案

Astd::ofstream仅用于输出，不能用它读取输入。

Astd::ifstream仅用于输入，您不能用它编写输出。

因此，您需要

• 使用单独的std::ofstream和std::ifstream变量：

  int main()
  {
      ofstream out_file;
      ifstream in_file;
      string line;
  
      out_file.open("beef.txt", ios_base::trunc);
      if (out_file.is_open())
      {
          out_file << "beef" << endl;
          out_file.close();
      }
  
      in_file.open("beef.txt");
      if (in_file.is_open())
      {
          getline(in_file, line);
          in_file.close();
  
          cout << "File contains:" << endl;
          cout << line << endl;
      }
  
      cout << "Enter what you would like to be contained in the file" << endl;
      getline(cin, line);
  
      out_file.open("beef.txt", ios_base::trunc);
      if (out_file.is_open())
      {
          out_file << line << endl;
          out_file.close();
      } 
  
      in_file.open("beef.txt");
      if (in_file.is_open())
      {
          getline(in_file, line);
          in_file.close();
  
          cout << "File now contains:" << endl;
          cout << line << endl;
      }
  
      return 0;
  }
  

• 根据调用open()时是否指定了in和/或out标志，使用一个std::fstream变量，该变量可同时用于输出和输入：

  int main()
  {
      fstream file;
      string line;
  
      file.open("beef.txt", ios_base::out | ios_base::trunc);
      if (file.is_open())
      {
          file << "beef" << endl;
          file.close();
      }
  
      file.open("beef.txt", ios_base::in);
      if (file.is_open())
      {
          getline(file, line);
          file.close();
  
          cout << "File contains:" << endl;
          cout << line << endl;
      }
  
      cout << "Enter what you would like to be contained in the file" << endl;
      getline(cin, line);
  
      file.open("beef.txt", ios_base::out | ios_base::trunc);
      if (file.is_open())
      {
          file << line << endl;
          file.close();
      }
  
      file.open("beef.txt", ios_base::in);
      if (in_file.is_open())
      {
          getline(in_file, line);
          in_file.close();
  
          cout << "File now contains:" << endl;
          cout << line << endl;
      }
  
      return 0;
  }
  

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