File Handling in C++ - Read and Write Files

File handling in C++ is essential for working with external data sources, such as reading data from files and writing data to files. C++ provides a set of file stream classes that make file I/O operations straightforward. In this guide, we'll explore the basics of file handling in C++.

Writing to a File

You can use the ofstream class to write data to a file. Here's how to write text to a file:

#include <iostream>
#include <fstream>
using namespace std;
int main() {
    ofstream outFile("output.txt");    if (outFile.is_open()) {
        outFile << "Hello, World!" << endl;
        outFile.close();
        cout << "Data written to the file." << endl;
    } else {
        cerr << "Error: Unable to open the file." << endl;
    }    return 0;
}
    

In this example, we create an ofstream object, open the file "output.txt," write data to it, and then close the file. If the file doesn't exist, it will be created.

Reading from a File

You can use the ifstream class to read data from a file. Here's how to read text from a file:

#include <iostream>
#include <fstream>
using namespace std;
int main() {
    ifstream inFile("input.txt");    if (inFile.is_open()) {
        string line;
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close();
    } else {
        cerr << "Error: Unable to open the file." << endl;
    }    return 0;
}
    

In this example, we create an ifstream object, open the file "input.txt," and read its content line by line, displaying it to the console.

Appending to a File

You can use the ofstream class in append mode to add content to an existing file without overwriting its existing content:

#include <iostream>
#include <fstream>
using namespace std;
int main() {
    ofstream outFile("output.txt", ios::app);    if (outFile.is_open()) {
        outFile << "Appending text to the file." << endl;
        outFile.close();
        cout << "Data appended to the file." << endl;
    } else {
        cerr << "Error: Unable to open the file." << endl;
    }    return 0;
}
    

In this example, we open the file "output.txt" in append mode using the ios::app flag and then append new content to it.

Conclusion

File handling is an important part of C++ programming, enabling you to work with external data sources. As you continue your C++ journey, you'll explore more advanced file handling techniques, such as binary file I/O and error handling.