Virtual Base Class

Virtual base classes in C++ programs are used in virtual inheritance in such a way that it prevents multiple "instances" of a given class from appearing in an inheritance hierarchy when making use of multiple inheritances.

Where can the Virtual base class be used?

Below are where the Virtual base class can be used

• In the case where are member functions with the same name in a base class and derived class, the virtual base class gives the programmer capability to call a member function of a different class by the same function call depending upon the different context. However, this feature in C++ programming is known as polymorphism and it is an important feature of OOP. 
• Secondly, if a base class and derived class have the same function and then you write a code to access that function using the pointer of the base class; the function in the base class is executed even if the object of a derived class is referenced with that pointer variable. 

Example:

#include <iostream>

class B
{
    public:
       void display()
         { cout<<"Content of base class.n"; }
};

class D : public B
{
    public:
       void display()
         { cout<<"Content of derived class.n"; }
};

void main()
{
    B *b;
    D d;
    b->display();

    b = &d;    /* Address of object d in pointer variable */
    b->display();
    getch();
}