Reading and Writing a file

Reading and Writing a File in C++

C++ provides a powerful set of file handling functions through the <fstream> header to:

• Write data to a file using ofstream
• Read data from a file using ifstream
• Do both using fstream

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🔧 Step-by-Step Process

1. Include the Required Header

#include <fstream>

2. Create a File Stream Object

• Use ofstream for writing
• Use ifstream for reading
• Use fstream for both

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✍️ Writing to a File

✅ Example: Writing Text to a File

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

int main() {
    ofstream outFile("myfile.txt");  // Open file in write mode

    if (outFile.is_open()) {
        outFile << "Hello BCA Students!\n";
        outFile << "This is C++ file writing example.\n";
        outFile.close();  // Close file
        cout << "Data written successfully!" << endl;
    } else {
        cout << "Failed to open the file." << endl;
    }

    return 0;
}

🔎 What It Does:

• Opens (or creates) myfile.txt
• Writes two lines to the file
• Closes the file

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📖 Reading from a File

✅ Example: Reading Text from a File Line by Line

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

int main() {
    ifstream inFile("myfile.txt");  // Open file in read mode
    string line;

    if (inFile.is_open()) {
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close();  // Close file
    } else {
        cout << "Unable to open the file." << endl;
    }

    return 0;
}

🔎 What It Does:

• Opens myfile.txt
• Reads each line using getline()
• Prints the content to the console

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💡 Reading and Writing Other Data Types

You can also read and write integers, floats, characters, etc.

✅ Writing Numbers

ofstream file("numbers.txt");
int a = 100;
float b = 25.75;
file << a << " " << b;
file.close();

✅ Reading Numbers

ifstream file("numbers.txt");
int x;
float y;
file >> x >> y;
cout << "x = " << x << ", y = " << y;
file.close();

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📦 Reading and Writing Using fstream (Both Read & Write)

#include <fstream>
using namespace std;

int main() {
    fstream file;
    file.open("data.txt", ios::out);  // write mode
    file << "BCA File Handling Example\n";
    file.close();

    file.open("data.txt", ios::in);   // read mode
    string line;
    while (getline(file, line)) {
        cout << line << endl;
    }
    file.close();

    return 0;
}

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📝 Summary Table

Operation	Stream Class	Function Used
Writing to file	ofstream	<<
Reading from file	ifstream	>> or getline()
Both read & write	fstream	<<, >>
Close a file	Any stream	.close()

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❗Best Practices

• Always check if the file is open before reading or writing.
• Always close the file after operations.
• Handle possible file errors using is_open() or error messages.