C++ Types of Inheritance

As we already know that inheritance is one of the most important pillar of object oriented programming.

C++ allows us to implement various inheritance models in a program. These inheritance models are,

1. Multilevel inheritance
2. Multiple inheritance
3. Hierarchical inheritance

Lets discuss them one by one.

---

Multilevel Inheritance

According to this model we can derive a class from a derived class which is derived from another derived class or base class. This forms layers of inheritance.

Syntax for multilevel inheritance

class A
{ 
... .. ...
};
class B: public A
{
... .. ...
};
class C: public B
{
... ... ...
};

In above syntax, we are deriving class B from base class A and from B class C is derived.

Lets take an example for better understanding

Example 1:

#include <iostream>
using namespace std;
class A
{
 public:
 void display()
 {
 cout<<"this is base class";
 }
};
class B : public A
{
};
class C : public B
{
};
int main()
{
 C obj;
 obj.display();
 return 0;
}

Output:

this is base class

in this program, we have three classes A,B and C deriving from each other respectively, when we called function of class C, we got function of A. this due to multilevel inheritance.

---

Multiple Inheritance

According to this model, a derived class can be derived from multiple base classes.

Lets understand it with an example

Example 2:

#include <iostream>
using namespace std;

class A
{
public:
 A() { cout << "A's constructor" << endl; }
};

class B
{
public:
 B() { cout << "B's constructor" << endl; }
};
 
class C: public B, public A
{
public:
 C() { cout << "C's constructor" << endl; }
};

int main()
{
 C c;
 return 0;
}

Output:

B’s constructor
A’s constructor
C’s constructor

in the above program, you can see both the classes A and B are inherited in class C.

Note: look at the order class C: public B, public A, that is why functions are inherited in the order as given in output.

---

Hierarchical Inheritance

According to this model, more than one classes can be derived from the base class.

Syntax of hierarchical inheritance is given below

class A {
 ... .. ...
}
class B: public A {
 ... .. ...
}
class C: public A {
 ... .. ...
}
class D: public A {
 ... .. ...
}