Examples of inheritance in c plus plus?

Answer 1

Single-inheritance is where one class inherits directly from another class:

class A {};

class B : public A {};

Here, class B inherits all the public and protected members of class A.

Multiple-inheritance is where one class inherits directly from two or more classes:

class A {};

class B {};

class C : public A, public B {};

Here, class C inherits all the public and protected members of both A and B.

Multi-level inheritance is where one class inherits from another class that itself derived.

class A {};

class B : public A {};

class C : public B {};

Here, class B inherits all the public and protected members of A while class C inherits all the public and protected members of B, including those inherited from A.

Virtual inheritance applies to multi-level inheritance whereby a virtual base class becomes a direct ancestor to the most-derived class. This variation of inheritance is typically used in multiple inheritance situations where two or more intermediate classes inherit from the same base class:

class A {};

class B : public virtual A {};

class C : public virtual A {};

class D : public B, public C {};

Here, classes B and C both inherit from class A. Without virtual inheritance this would mean class D would inherit two instances of A (B::A and C::A), thus creating ambiguity when referring to D::A. By employing virtual inheritance, D inherits directly from A, and both B and C inherit from D::A. In other words, B and C share the same instance of A.

Another use of virtual inheritance is when you need to make a class final.

class A;

class B

{

friend class A;

B() {} // private constructor

};

class A : public virtual B

{

};

Here, class A is the final class. Class B is a helper class that has a private constructor while class A is declared a friend of class B. Class A is therefore the only class that can inherit from class B as it is the only class that can construct objects from class B. However, by inheriting class B virtually, we ensure that no other class can be derived from class A because virtual inheritance ensures that the most-derived class must be able to construct a class B object first. Currently, only class A has that privilege and must always be the most-derived class.