Normally you will have to explicitly declare your own destructor if:
1.You are declaring a class which is supposed to serve as a base for inheritance involving polymorphism, if you do you'll need a virtual destructor to make sure that the destructor of a Derived class is called upon destroying it through a pointer/reference to Base.
2.You need to release resourced aquired by the class during its leftime
Example 1: The class has a handle to a file, this needs to be closed when the object destructs; the destructor is the perfect location.
Exempel 2: The class owns an object with dynamic-storage duration, since the lifetime of the object can potentially live on long after the class instance has been destroyed you'll need to explicitly destroy it in the destructor.
leetcode (3)