Opening and Closing File

📘 File Handling in C++

File handling allows a C++ program to create, read, write, and manipulate files stored on the disk.

To perform file operations, C++ provides file stream classes from the <fstream> header:

Stream Class	Purpose
ifstream	Input file stream (read from file)
ofstream	Output file stream (write to file)
fstream	Input and output stream (read & write)

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🔑 Opening a File in C++

To open a file, you create a stream object and use either:

1. Constructor method
2. open() function

✅ 1. Using Constructor

ofstream outFile("data.txt");     // Opens file for writing
ifstream inFile("data.txt");      // Opens file for reading

✅ 2. Using open() function

ofstream outFile;
outFile.open("data.txt");         // Opens file for writing

You can also specify file modes (more below).

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✍️ Example: Writing to a File

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

int main() {
    ofstream outFile("example.txt");  // Open for writing

    if (outFile.is_open()) {
        outFile << "Hello, file handling in C++!\n";
        outFile << "Writing to a file.\n";
        outFile.close();  // Always close the file
        cout << "Data written successfully!" << endl;
    } else {
        cout << "File could not be opened." << endl;
    }

    return 0;
}

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✍️ Example: Reading from a File

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

int main() {
    ifstream inFile("example.txt");  // Open for reading
    string line;

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

    return 0;
}

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📌 File Modes in C++

When opening a file, you can use file mode flags with open():

Mode	Description
ios::in	Open for reading
ios::out	Open for writing
ios::app	Append to end of file
ios::trunc	Truncate file if it exists
ios::binary	Open in binary mode

🧪 Example:

fstream file;
file.open("data.txt", ios::in | ios::out);  // Read & write

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✅ Closing a File

Always close a file after finishing operations using .close():

file.close();

Closing a file:

• Saves data to disk (if writing)
• Frees system resources
• Avoids file corruption

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📝 Summary

Action	Method
Open file (write)	ofstream out("file.txt");
Open file (read)	ifstream in("file.txt");
Open with mode	file.open("file.txt", mode);
Close file	file.close();