C++ Coding Standards: 101 Rules, Guidelines, and Best Practices

50. Make base class destructors public and virtual, or protected and nonvirtual

Summary

To delete, or not to delete; that is the question: If deletion through a pointer to a base Base should be allowed, then Base’s destructor must be public and virtual. Otherwise, it should be protected and nonvirtual.

Discussion

This simple guideline illustrates a subtle issue and reflects modern uses of inheritance and object-oriented design principles.

For a base class Base, calling code might try to delete derived objects through pointers to Base. If Base’s destructor is public and nonvirtual (the default), it can be accidentally called on a pointer that actually points to a derived object, in which case the behavior of the attempted deletion is undefined. ...