Exception Handling & File I/O

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

// Custom exception
class FileError : public runtime_error {
    string filename;
public:
    FileError(const string &file, const string &msg)
        : runtime_error(msg), filename(file) {}
    const string &getFilename() const { return filename; }
};

// Function that throws
double divide(double a, double b) {
    if (b == 0.0) throw invalid_argument("Division by zero");
    return a / b;
}

void writeFile(const string &filename, const string &content) {
    ofstream file(filename);
    if (!file.is_open()) {
        throw FileError(filename, "Cannot open file for writing");
    }
    file << content;
    // File automatically closed by destructor (RAII)
}

string readFile(const string &filename) {
    ifstream file(filename);
    if (!file.is_open()) {
        throw FileError(filename, "Cannot open file for reading");
    }
    string content((istreambuf_iterator<char>(file)),
                     istreambuf_iterator<char>());
    return content;
}

int main() {
    // Exception handling
    try {
        cout << divide(10, 3) << endl;  // Works fine
        cout << divide(10, 0) << endl;  // Throws!
    } catch (const invalid_argument &e) {
        cerr << "Error: " << e.what() << endl;
    }

    // File I/O with exception handling
    try {
        writeFile("test.txt", "Hello, C++ File I/O!");
        string content = readFile("test.txt");
        cout << "Read: " << content << endl;
    } catch (const FileError &e) {
        cerr << "File error (" << e.getFilename() << "): " << e.what() << endl;
    } catch (const exception &e) {
        cerr << "Error: " << e.what() << endl;
    }

    return 0;
}