File Handling

1. File Stream Classes

• ofstream: Output file stream (writing to files)
• ifstream: Input file stream (reading from files)
• fstream: File stream (both reading and writing)

2. File Modes

3. Writing to Files

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

int main() {
    // Method 1: Using ofstream
    ofstream outFile;
    outFile.open("data.txt");
    
    if (outFile.is_open()) {
        outFile << "Hello, World!" << endl;
        outFile << "This is a file." << endl;
        outFile.close();
    } else {
        cout << "Error opening file!" << endl;
    }
    
    // Method 2: Direct initialization
    ofstream outFile2("data2.txt");
    outFile2 << "Line 1" << endl;
    outFile2 << "Line 2" << endl;
    outFile2.close();
    
    return 0;
}

4. Reading from Files

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

int main() {
    // Method 1: Using ifstream
    ifstream inFile;
    inFile.open("data.txt");
    
    if (inFile.is_open()) {
        string line;
        while (getline(inFile, line)) {
            cout << line << endl;
        }
        inFile.close();
    } else {
        cout << "Error opening file!" << endl;
    }
    
    // Method 2: Reading word by word
    ifstream inFile2("data.txt");
    string word;
    while (inFile2 >> word) {
        cout << word << " ";
    }
    inFile2.close();
    
    return 0;
}

5. Reading and Writing

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

int main() {
    fstream file;
    file.open("data.txt", ios::in | ios::out);
    
    if (file.is_open()) {
        // Write
        file << "Hello" << endl;
        file << "World" << endl;
        
        // Read
        file.seekg(0);  // Move to beginning
        string line;
        while (getline(file, line)) {
            cout << line << endl;
        }
        
        file.close();
    }
    
    return 0;
}

6. File Position Pointers

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

int main() {
    fstream file("data.txt", ios::in | ios::out);
    
    // Get current position
    streampos pos = file.tellg();
    cout << "Current position: " << pos << endl;
    
    // Move to beginning
    file.seekg(0, ios::beg);
    
    // Move to end
    file.seekg(0, ios::end);
    
    // Move relative
    file.seekg(10, ios::cur);  // 10 bytes forward
    
    file.close();
    return 0;
}

7. Binary File Operations

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

struct Student {
    int rollNo;
    char name[50];
    float marks;
};

int main() {
    // Writing binary file
    ofstream outFile("students.dat", ios::binary);
    Student s1 = {101, "John", 85.5};
    outFile.write((char*)&s1, sizeof(Student));
    outFile.close();
    
    // Reading binary file
    ifstream inFile("students.dat", ios::binary);
    Student s2;
    inFile.read((char*)&s2, sizeof(Student));
    cout << s2.rollNo << " " << s2.name << " " << s2.marks << endl;
    inFile.close();
    
    return 0;
}

8. File Error Handling

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

int main() {
    ifstream file("nonexistent.txt");
    
    if (!file) {
        cout << "File not found!" << endl;
        return 1;
    }
    
    if (file.fail()) {
        cout << "File operation failed!" << endl;
    }
    
    if (file.bad()) {
        cout << "Fatal error!" << endl;
    }
    
    if (file.eof()) {
        cout << "End of file reached" << endl;
    }
    
    file.close();
    return 0;
}

9. Complete Example

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

int main() {
    // Write student data
    ofstream outFile("students.txt");
    if (outFile.is_open()) {
        outFile << "101 John 85.5" << endl;
        outFile << "102 Alice 90.0" << endl;
        outFile << "103 Bob 78.5" << endl;
        outFile.close();
    }
    
    // Read and display
    ifstream inFile("students.txt");
    if (inFile.is_open()) {
        int rollNo;
        string name;
        float marks;
        
        while (inFile >> rollNo >> name >> marks) {
            cout << rollNo << " " << name << " " << marks << endl;
        }
        inFile.close();
    }
    
    return 0;
}