pure-virtual

Possible Duplicate: C++ Virtual/Pure Virtual Explained What is the difference between a pure virtual function and a virtual function? I know "Pure Virtual Function is a Virtual function with no body", but what does this mean and what is actually done by the line below: virtual void virtualfunctioname() = 0 sbi A virtual function makes its class a polymorphic base class . Derived classes can override virtual functions. Virtual functions called through base class pointers/references will be resolved at run-time. That is, the dynamic type of the object is used instead of its static type : Derived

I sometimes notice programs that crash on my computer with the error: "pure virtual function call". How do these programs even compile when an object cannot be created of an abstract class? Adam Rosenfield They can result if you try to make a virtual function call from a constructor or destructor. Since you can't make a virtual function call from a constructor or destructor (the derived class object hasn't been constructed or has already been destroyed), it calls the base class version, which in the case of a pure virtual function, doesn't exist. (See live demo here ) class Base { public: Base

I understand the need for a virtual destructor. But why do we need a pure virtual destructor? In one of the C++ articles, the author has mentioned that we use pure virtual destructor when we want to make a class abstract. But we can make a class abstract by making any of the member functions as pure virtual. So my questions are When do we really make a destructor pure virtual? Can anybody give a good real time example? When we are creating abstract classes is it a good practice to make the destructor also pure virtual? If yes..then why? Motti Probably the real reason that pure virtual

We always declare a pure virtual function as: virtual void fun () = 0 ; I.e., it is always assigned to 0. What I understand is that this is to initialize the vtable entry for this function to NULL and any other value here results in a compile time error. Is this understanding correct or not? The reason =0 is used is that Bjarne Stroustrup didn't think he could get another keyword, such as "pure" past the C++ community at the time the feature was being implemented. This is described in his book, The Design & Evolution of C++ , section 13.2.3: The curious =0 syntax was chosen ... because at the