Shared ownership means that an object can have multiple owners. When the last owner ceases to exist, the object will be deleted. This is a very useful pointer type, but is also more complicated than unique pointer.
The std::shared_ptr object uses reference counting to keep track of the number of owners an object has. When the counter reaches 0, the object will be deleted. The counter needs to be stored somewhere, so it does have some memory overhead compared with the unique pointer. Also, std::shared_ptr is thread-safe, so the counter needs to be updated atomically to prevent race conditions.
The recommended way of creating objects owned by shared pointers is to use std::make_shared(). It is both safer (from an exception-safety ...
