Try It Yourself - SyntaxStudy Editor

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#include <iostream>
#include <fstream>
#include <stdexcept>

// RAII file wrapper
class FileHandle {
public:
    explicit FileHandle(const char* path, const char* mode) {
        file_ = std::fopen(path, mode);
        if (!file_) throw std::runtime_error("Cannot open file");
        std::cout << "File opened
";
    }

~FileHandle() {
        if (file_) {
            std::fclose(file_);
            std::cout << "File closed
";  // always runs
        }
    }

// Prevent copy
    FileHandle(const FileHandle&)            = delete;
    FileHandle& operator=(const FileHandle&) = delete;

FILE* get() const { return file_; }

private:
    FILE* file_;
};

// RAII mutex simulation
struct MutexLock {
    explicit MutexLock(bool& mutex) : mutex_(mutex) {
        mutex_ = true;
        std::cout << "Lock acquired
";
    }
    ~MutexLock() {
        mutex_ = false;
        std::cout << "Lock released
";
    }
    bool& mutex_;
};

int main() {
    bool mutex = false;

{
        MutexLock lock(mutex);
        std::cout << "Critical section
";
        // lock released automatically at end of block
    }

// FileHandle example (file may not exist in demo)
    try {
        FileHandle fh("demo.txt", "w");
        std::fputs("Hello RAII
", fh.get());
        // file closed automatically even if exception thrown
    } catch (const std::exception& e) {
        std::cout << "Error: " << e.what() << "
";
    }

return 0;
}