Just like websites store user data through form submissions, C++ allows you to read data from and write data to files for similar purposes.

Reading from and writing to files in C++ is accomplished using file streams, which are quite similar to the cout and cin streams you are already familiar with. C++ provides two types of file streams: ofstream for writing to files, and ifstream for reading from files.

In the provided C++ code, we first write to a file "example.txt" using an ofstream object. This file is created in the same directory as our C++ program. We then read from the same file using an ifstream object, printing its contents to the console.

This technology allows user data to be saved and used across different sessions, similar to how cookies and local storage work in web development. It's an essential concept in building C++ applications that persist user data or read in large datasets for machine learning, financial analysis, and AI modeling.

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#include <fstream>

#include <iostream>

using namespace std;

int main() {

  // create a file

  ofstream file1("example.txt");

  file1 << "Writing this to a file.\n";

  file1.close();

​

  // read from a file

  string line;

  ifstream file2("example.txt");

  if (file2.is_open()) {

    while (getline (file2, line)) {

      cout << line << '\n';

    }

    file2.close();

  } else cout << "Unable to open file"; 

  return 0;

}