RAII

Code

#include <iostream>
#include <fstream>
#include <mutex>

// RAII class: acquire on construct, release on destruct
class FileGuard {
    FILE* file;
public:
    explicit FileGuard(const char* path) {
        file = fopen(path, "r");
        if (!file) throw std::runtime_error("Cannot open file");
    }
    ~FileGuard() {
        if (file) fclose(file);
    }
    // Disable copy
    FileGuard(const FileGuard&) = delete;
    FileGuard& operator=(const FileGuard&) = delete;
    FILE* get() { return file; }
};

// lock_guard uses RAII
std::mutex mtx;
void safe_increment(int& counter) {
    std::lock_guard<std::mutex> lock(mtx);
    counter++;
} // Auto unlock

int main() {
    {
        FileGuard fg("example.txt");
        // Use fg.get() to read file
    } // fg destructor auto-closes file

    {
        std::ofstream out("temp.txt");
        out << "Hello RAII";
    } // Auto close file

    return 0;
}

Explanation

RAII binds resources to object lifetime, acquiring on construction and releasing on destruction, ensuring exception safety.

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