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C++ Files


C++ Files

The fstream library allows us to work with files.

To use the fstream library, include both the standard <iostream> AND the <fstream> header file:

Example

#include <iostream>
#include <fstream>

There are three classes included in the fstream library, which are used to create, write or read files:

Class Description
ofstream Creates and writes to files
ifstream Reads from files
fstream A combination of ofstream and ifstream: creates, reads, and writes to files

Create and Write To a File

To create a file, use either the ofstream or fstream class, and specify the name of the file.

To write to the file, use the insertion operator (<<).

Example

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

int main() {
  // Create and open a text file
  ofstream MyFile("filename.txt");

  // Write to the file
  MyFile << "Files can be tricky, but it is fun enough!";

  // Close the file
  MyFile.close();
}

Why do we close the file?

It is considered good practice, and it can clean up unnecessary memory space.


Read a File

To read from a file, use either the ifstream or fstream class, and the name of the file.

Note that we also use a while loop together with the getline() function (which belongs to the ifstream class) to read the file line by line, and to print the content of the file:

Example

// Create a text string, which is used to output the text file
string myText;

// Read from the text file
ifstream MyReadFile("filename.txt");

// Use a while loop together with the getline() function to read the file line by line
while (getline (MyReadFile, myText)) {
  // Output the text from the file
  cout << myText;
}

// Close the file
MyReadFile.close();
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