Exception Safety Guarantees

Before diving into handling exceptions with smart pointers, it’s essential to understand exception safety guarantees provided by C++. There are three levels of exception safety:

1. No-throw guarantee: The operation will never throw an exception.
2. Strong exception safety guarantee: If an exception occurs, the object’s state will remain unchanged.
3. Basic exception safety guarantee: If an exception occurs, the object’s state may be modified but remains in a valid and usable state.

Using std::unique_ptr

std::unique_ptr provides a lightweight mechanism for exclusive ownership of a dynamically allocated object. When an exception is thrown during object construction, the memory allocated by std::unique_ptr is automatically deallocated, ensuring proper resource cleanup. However, if an exception is thrown in the constructor of the pointed object, the std::unique_ptr itself will not be destroyed. To handle such exceptions, you can use the following approach:

std::unique_ptr<MyClass> createMyClass() {
    std::unique_ptr<MyClass> ptr;
    try {
        ptr = std::make_unique<MyClass>(); // Potential exception
        ptr->initialize(); // Potential exception
    } catch (...) {
        // Handle exception
        throw; // Re-throw the exception
    }
    return ptr;
}

In the above code snippet, we create a std::unique_ptr called ptr and initialize it within a try block. If an exception occurs during the object creation or initialization, the catch block is executed. Here, you can handle the exception as needed and re-throw it to maintain exception safety.

Using std::shared_ptr

std::shared_ptr allows multiple pointers to share ownership of the same object. When an exception is thrown during object construction or destruction, the std::shared_ptr automatically deallocates the memory, ensuring proper cleanup.

std::shared_ptr<MyClass> createMyClass() {
    std::shared_ptr<MyClass> ptr;
    try {
        ptr = std::make_shared<MyClass>(); // Potential exception
        ptr->initialize(); // Potential exception
    } catch (...) {
        // Handle exception
        throw; // Re-throw the exception
    }
    return ptr;
}

Similarly to std::unique_ptr, when using std::shared_ptr, we should enclose the construction and initialization of the object within a try block and handle any potential exceptions that may occur.

Conclusion

When using smart pointers like std::unique_ptr and std::shared_ptr, it’s important to handle exceptions properly to ensure resource cleanup. By enclosing object construction and initialization within a try block and handling any potential exceptions, we can achieve robust and exception-safe code. Remember, exception safety guarantees are vital for writing reliable and maintainable software.

#C++ #ExceptionHandling #SmartPointers