title: “C++: Exploring std::shared_ptr and Exception Safety” date: “2021-09-13” description: “Learn how to use std::shared_ptr and ensure exception safety in your C++ code.” tags: [C++, std::shared_ptr, exception safety] —

In C++, managing memory is an essential aspect of writing robust and error-free code. The std::shared_ptr class from the C++ Standard Library provides a convenient and safe way to manage dynamically allocated objects. In this blog post, we will explore the usage of std::shared_ptr and discuss how to ensure exception safety when using it.

Understanding std::shared_ptr

std::shared_ptr is a smart pointer that retains shared ownership of an object through a pointer. Multiple std::shared_ptr instances can point to the same object, keeping a reference count internally. The object will be automatically deleted when the last std::shared_ptr pointing to it gets destroyed.

You can create a std::shared_ptr by using the std::make_shared function or directly assigning a pointer to it. Let’s see an example:

#include <memory>

void foo() {
    // Creating a shared_ptr using make_shared
    std::shared_ptr<int> ptr1 = std::make_shared<int>(42);

    // Creating a shared_ptr from raw pointer
    std::shared_ptr<int> ptr2(new int(21));
}

In the above code snippet, we create two std::shared_ptr instances ptr1 and ptr2 pointing to different int objects. It’s important to note that you should avoid using new directly with shared_ptr to avoid potential resource leaks due to exception throws.

Exception Safety with std::shared_ptr

Achieving exception safety is crucial to ensure your code behaves correctly even when exceptions are thrown. When using std::shared_ptr, we need to consider a few guidelines to maintain exception safety:

1. Use std::make_shared for avoiding memory leaks: The std::make_shared function internally manages memory allocation and reference counting. Using it helps to avoid potential memory leaks if an exception occurs during construction.

2. Avoid using naked new with std::shared_ptr: Directly assigning a raw pointer created using new to a std::shared_ptr can result in resource leaks if exceptions are thrown before the std::shared_ptr construction. Always prefer std::make_shared or std::shared_ptr constructor to initialize pointers.

3. Wrap potentially throwing operations with exception-safe constructs: If you have operations that can throw exceptions, it’s a good practice to wrap them with exception-safe constructs such as try-catch blocks or appropriate exception handling mechanisms. This ensures that resource clean-up is properly handled.

void foo() {
    std::shared_ptr<int> ptr;
    try {
        // Perform potentially throwing operation
        ptr = std::make_shared<int>(42);
        // Other code that might throw exceptions
    }
    catch (...) {
        // Handle exceptions
        // Release allocated resources, if necessary
    }
}

By following these guidelines, you can ensure that your code using std::shared_ptr remains exception-safe and handles exceptions gracefully without causing resource leaks.

Conclusion

std::shared_ptr is a powerful tool in C++ for managing memory and ensuring automatic resource cleanup. By understanding its usage and considering exception safety, you can write more robust and reliable code. Remember to use std::make_shared and avoid naked new to minimize the chances of resource leaks. Wrap potentially throwing operations with proper exception handling to maintain exception safety in your code.

Keep learning and exploring the various features of C++ to become a more proficient developer!

#C++ #std.shared_ptr #exception-safety