template<class D, class T>
D* get_deleter(const shared_ptr<T>& p) noexcept;
Returns: If p owns a deleter d of type cv-unqualified D, returns addressof(d); otherwise returns nullptr. The returned pointer remains valid as long as there exists a shared_ptr instance that owns d. [ Note: It is unspecified whether the pointer remains valid longer than that. This can happen if the implementation doesn't destroy the deleter until all weak_ptr instances that share ownership with p have been destroyed. — end note ]