Re: Abstract base class / virtual destructor

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 08 Aug 2006 10:41:11 +0200

Message-ID:

<6avlq3-ejt.ln1@satorlaser.homedns.org>

Headache wrote:

If I have a totally abstract base class A (essentially an interface):

class A
{
   virtual void DoSomething() = 0;
}

and I have a derived class B
{
   int m_Bint;
   virtual void DoSomething();
}

Importantly, it is known that class B does not allocate memory on the
heap.

Irrelevant.

is it absolutely correct, good-manners or incorrect to include a
virtual destructor in base class A?

There is a simple rule about destructors: if you plan to polymorphically
delete the object (i.e. call delete on a pointer-to-base) you must
absolutely have a virtual dtor. Typically there are three cases
1. non-baseclass
This one is not for derivation and doesn't need a virtual dtor.
2. public, virtual dtor
For cases where you want to polymorphically delete an object.
3. protected, nonvirtual dtor
You can still derive from this, but you can't delete via a
pointer-to-baseclass.

For the case:

A* p = new B;

This is not a problem, the problem is when and how you invoke delete.

Uli