C++17 STL Cookbook

Automatically handling shared heap memory with std::shared_ptr

In the last recipe, we learned how to use unique_ptr. This is an enormously useful and important class because it helps us manage dynamically allocated objects. However, it can only handle single ownership. It is not possible to let multiple objects own the same dynamically allocated object because, then, it would be unclear who has to delete it later.

The pointer type, shared_ptr, was designed for specifically this case. Shared pointers can be copied arbitrarily often. An internal reference counting mechanism tracks how many objects are still maintaining a pointer to the payload object. Only the last shared pointer that goes out of scope will call delete on the payload object. ...