15.24.txt

Exercise 15.24: What kinds of classes need a virtual destructor? What
operations must a virtual destructor perform?

By Faisal Saadatmand

Classes that are related by inheritance. The destructors of such classes are
responsible for freeing the resources of their objects. The base class must
define a virtual destructor, which may be overridden by the derived classes.
This is important so that compiler knows which destructor to call when an
object of these classes is destroyed.

This is especially important when dealing with objects of polymorphic types,
objects whose static and dynamic types can differ, as in the case with classes
related by inheritance. (p. 605) Designating the destructor as virtual tells
the compiler to generate code that will resolve which destructor to run based
on dynamic type of the object at runtime, as opposed to the static type at
compile time, as what would happen if destructor were a non-virtual functions.
This will ensure that the appropriate destructor is called with such types.

Furthermore, if a derived class allocates memory on the heap, it must override
the base class virtual destructor to include the necessary steps to free the
resources it has allocated for its members.