File I/O

Overview

The standard workflow for File I/O is: Open -> Check if open -> Perform I/O -> Close. Closing is crucial to free up OS file locks and flush buffers.

Syntax

cpp

#include <fstream>
using namespace std;

ofstream file("log.txt");
if (file.is_open()) {
    file << "Line 1\n";
    file.close(); // Mandatory cleanup
}

Common Pitfalls

Using `cin >> str` or `file >> str` to read a sentence. It stops at the first space. Always use `getline(file, str)` to read full lines.

Interview Tips

Due to RAII in C++, the destructor of `ofstream`/`ifstream` automatically closes the file when the object goes out of scope. However, calling `.close()` manually is still good practice to catch write errors.

Real-World Example

Reading a file line-by-line.

example

cpp

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

int main() {
    ifstream inFile("document.txt");
    string line;
    
    if (inFile.is_open()) {
        // Read until EOF
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close();
    } else {
        cout << "Could not open file." << endl;
    }
    return 0;
}

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