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 preceding the base class’ name with the word virtual.
Consider following example:
class B : virtual public A
class C: virtual public A
class D: public B, public C
ob.i = 10; //unambiguous since only one copy of i is inherited.
ob.j = 20;
ob.k = 30;
ob.sum = ob.i + ob.j + ob.k;
cout << “Value of i is : ”<< ob.i<<”n”;
cout << “Value of j is : ”<< ob.j<<”n”; cout << “Value of k is :”<< ob.k<<”n”;
cout << “Sum is : ”<< ob.sum <<”n”;