Re: abstract base class question

From:

"rami" <onewastedlife@gmail.com>

Newsgroups:

comp.lang.c++

Date:

9 Jul 2006 03:11:48 -0700

Message-ID:

<1152439908.297459.260900@35g2000cwc.googlegroups.com>

Rolf Magnus wrote:

junw2000@gmail.com wrote:

Is it possible to create an abstract base class without a pure virtual
function?

Well, there are way to make one that behaves similiar, but why would you
want to? You can always make the destructor pure if there is no other
member function that you could make pure.

Thats correct!
To elaborate more on Rolfs point,
A pure virtual function can have body but it can only be called from
the derived classes and not by user directly. So for example:

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

void a::fun() { _DO_SOMETHING_}

class B : public A {
  void fun() {
     A::fun(); // works fine
  }
};

void main() {
   A myA; // fails as the class is abstract..

   B myB;
   myB.fun(); // works fine
}

Now that said, If you dont want any function to be pure virtual it
means you intend to call them through derived class objects. In this
case you can make destructor pure virtual and provide it a body as well
because when ur class is extended (which it must since it is abstract)
it will be destroyed properly since destructor will always be called
through the derived class destructor which c++ compiler will allow.

Ramneek