File Handling in C++ | C++ Programming Tutorial

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Your guide to understanding file handling in C++.

File Handling in C++

File handling in C++ involves reading from and writing to files. C++ provides file stream classes to perform file I/O operations: ifstream for reading files, ofstream for writing files, and fstream for both reading and writing.

1. Opening a File

To open a file, you need to create an object of the appropriate file stream class and associate it with a file using the open() method or by specifying the file name when creating the object.


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

int main() {
    ofstream outFile("example.txt"); // Open for writing
    if (outFile.is_open()) {
        outFile << "Writing to a file.\n";
        outFile.close(); // Close the file
    } else {
        cout << "Unable to open file for writing." << endl;
    }

    ifstream inFile("example.txt"); // Open for reading
    if (inFile.is_open()) {
        string line;
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close(); // Close the file
    } else {
        cout << "Unable to open file for reading." << endl;
    }

    return 0;
}

2. Reading from a File

To read data from a file, use the ifstream class. You can read the entire file line by line using getline(), or you can use the extraction operator >> for formatted input.


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

int main() {
    ifstream inFile("example.txt"); // Open file for reading
    if (inFile.is_open()) {
        string line;
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close(); // Close the file
    } else {
        cout << "Unable to open file." << endl;
    }
    return 0;
}

3. Writing to a File

To write data to a file, use the ofstream class. You can write strings, numbers, and other data types using the insertion operator <<.


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

int main() {
    ofstream outFile("example.txt"); // Open file for writing
    if (outFile.is_open()) {
        outFile << "This is a line of text." << endl;
        outFile << "This is another line." << endl;
        outFile.close(); // Close the file
    } else {
        cout << "Unable to open file." << endl;
    }
    return 0;
}

4. Appending to a File

To append data to an existing file, open the file in append mode by using the ios::app mode flag.


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

int main() {
    ofstream outFile("example.txt", ios::app); // Open for appending
    if (outFile.is_open()) {
        outFile << "Appending a new line." << endl;
        outFile.close(); // Close the file
    } else {
        cout << "Unable to open file." << endl;
    }
    return 0;
}

5. File Modes

Different file modes can be used to control how a file is opened:

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