C++ Files

C++ Files (File Handling)

To write to or read from files in C++, you need to use the <fstream> library.

This library provides three main classes for file handling:

• ofstream - Creates and writes to files (Output file stream)
• ifstream - Reads from files (Input file stream)
• fstream - A combination of both; can create, read, and write to files.

1. Writing to a File

To create a file and write to it, use the ofstream class.

#include <iostream>
#include <fstream> // Include fstream library
using namespace std;

int main() {
  // Create and open a text file
  ofstream MyWriteFile("filename.txt");
  // Write text to the file using the insertion operator (<<)
  MyWriteFile << "Files can be tricky, but it is fun enough!";
  // Close the file when done
  MyWriteFile.close();
  cout << "File written successfully.\n";
  return 0;
}

Why close the file? Always use .close() when you are done. It frees up memory and system resources, and ensures that the data is physically saved to the hard drive.

2. Reading from a File

To read from an existing file, use the ifstream class and a while loop together with the getline() function to read the file line by line.

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main() {
  // Create a text string variable to hold each line from the file
  string myText;
  // Read from the text file
  ifstream MyReadFile("filename.txt");
  // Use a while loop together with getline() to read file line by line
  while (getline(MyReadFile, myText)) {
    // Output the text from the file
    cout << myText << "\n";
  }
  // Close the file
  MyReadFile.close();
  return 0;
}

If you try to read a file that doesn't exist, C++ will not crash, but the while loop will never execute. It is good practice to check if the file opened successfully using if (MyReadFile.is_open()).