Inheritance Part 3, Virtual Base Class

Virtual Base Class:

When two or more objects are derived from a common base class, we can prevent multiple copies of the base class being present in an object derived from those objects by declaring the base class as virtual when it is being inherited. Such a base class is known as virtual base class. This can be achieved by proceeding the base class name with virtual.

Ex:

class a

{

            ---

            ---

};

class b: virtual public a

{

            ----

            ----

};

class c:virtual public a

{

            ----

            ----

};

class d:public b,public c

{

            ----

            ----

};

 

In this example, classes B and C inherit features from class A.

Derived class D inherits features from classes B and C.

Derived class D inherits features of class A twice through classes B and C

To solve this problem derived class B and C should be declared as virtual.

 

Abstract classes:

An abstract class is one that is not used to create objects

This class is designed only to act as a base class.

 

Constructors and destructors in Inheritance:

When both derived class and base class contains constructors, the base class constructor is executed first and then constructer in the derived class is executed.

When both derived class and base class contains destructor, the derived class destructor is executed first, and then destructor of base class is executed.