FAQ 21.05 Can destructors be virtual?

Yes, many destructors should be virtual.

Virtual destructors are extremely valuable when some derived classes have specified cleanup code. A practical, easy-to-remember guideline: if a class has any virtual functions, it should have a virtual destructor. The rationale for this is that if a class has no virtual functions, chances are the class designer wasn't planning on the class being used as a base class, so a virtual destructor is unnecessary.

Furthermore, on most compilers there is no additional per-object space cost after the first virtual function, so there is very little reason not to make the destructor virtual if the class already has at least one virtual function.

Note that this guideline is not precise enough for every circumstance, but the precise rule is much harder to remember. Here is the more precise rule: if any derived class (or any data member and/or base class of any derived class, or any base class of any data member of any data member of any derived class, or any data member of any base class of any data member of any derived class and all other recursive combinations of base classes and data members) has (or will ever have) a nontrivial destructor, and if any code anywhere deletes (or will ever delete) that derived class object via a base class pointer, then the base class's destructor needs to be virtual.