Every abstract class should either have a, protected destructor, or, virtual destructor. If you’ve got a public non-virtual destructor, that’s no good, since it allows users to delete through that pointer a derived object. Since as we all know, that’s undefined behavior. For an abstract class, you already need a virtual-table pointer in the object, … Read more
Yes, they are the same. The derived class not declaring something virtual does not stop it from being virtual. There is, in fact, no way to stop any method (destructor included) from being virtual in a derived class if it was virtual in a base class. In >=C++11 you can use final to prevent it … Read more
You need virtual destructor when at least one of class methods is virtual. This is because the reason for virtual method is that you want to use polymorphism. Meaning you will call a method on the base class pointer and you want the most derived implementation – this is the whole point of polymorphism. Now … Read more
when/why should I use a virtual destructor? Follow Herb Sutters guideline: A base class destructor should be either public and virtual, or protected and nonvirtual Can this be classified as an undefined behavior (we are aware that ~D() is not going to be called for sure) ? It is Undefined Behavior as per the standard, … Read more
It’s even more important for an interface. Any user of your class will probably hold a pointer to the interface, not a pointer to the concrete implementation. When they come to delete it, if the destructor is non-virtual, they will call the interface’s destructor (or the compiler-provided default, if you didn’t specify one), not the … Read more
Virtual destructors are useful when you might potentially delete an instance of a derived class through a pointer to base class: class Base { // some virtual methods }; class Derived : public Base { ~Derived() { // Do some important cleanup } }; Here, you’ll notice that I didn’t declare Base’s destructor to be … Read more