Using ifstream, ofstream and fstream

Question

1. Trying to read into a file the word, "beef"

2. Later going and editing the contents of the file to whatever to user wants which will be stored in the string, "line"

3. The file never displays and when I go to check it manually, the text file is blank.

#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;
}

Answer 1

A std::ofstream is for output only, you can't read input with it.

A std::ifstream is for input only, you can't write output with it.

So, you need to either

• use separate std::ofstream and std::ifstream variables:

  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;
  }
  

• use a single std::fstream variable, which can be used for both output and input, depending on whether you specify in and/or out flags when calling open():

  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;
  }
  

Answer 2

In this snippet:

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

You create another ofstream object:

ofstream file1;

This shadows the one you had already created before. Moreover, the one you are shadowing now is the object that contains a valid file pointer to "beef.txt". Using the new inner-scope file1 doesn't point to any file yet, thus writing to it won't give you any results in "beef.txt".

Remove it to use the correct object:

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