Virtual base class
1 minute read
When ambiguity will arise in the hybrid inheritance? How we can remove it?
OR
When do we make a class virtual? OR What is a virtual base class? OR diamond shape inheritance.
v In a multipath inheritance (Hybrid inheritance) ambiguity is arise, because in this the sub class would have the duplicate sets of the members inherited from the base class (grandparent).
v The duplication of inherited members due to the multiple paths can be removed by making the common base class as virtual base class while declaring the direct or intermediate base classes.
v Virtual base class is a class that makes only one copy of that class inherited, regardless of how many inheritance paths exist between the virtual base class and a derived class.
v To make a class virtual, virtual keyword is used.
v For example: consider the following situation
v The ‘child’ has two direct base classes ‘parents1’ and ‘parents2’ which themselves have a common base class ‘grandparent’. The ‘child’ inherits the traits of ‘grandparents’ via two separate paths. It can also inherit directly. The ‘grandparent’ sometimes referred to as indirect base class.
v All the public and protected members of ‘grandparent’ are inherited into ‘child’ twice, first via ‘parent1’ and second via ‘parent2’. It means, ‘child’ would have duplicate sets of the members inherited from ‘grandparent’.
v To avoid this situation use virtual keyword.
v figure
v For example: consider the following statements
Class A //grand parent
{
. . . . .
. . . . .
};
Class B1 : virtual public A //parent1
{
. . . . .
. . . . .
};
Class B2 : public virtual A //parent2
{
. . . . .
. . . . .
};
Class C : public B1, public B2 //child
{
. . . . . //only one copy of A
. . . . . //will be inherited
};