C++ Inheritance

In C++, inheritance is a process in which one object acquires all the properties and behaviors of its parent object automatically. In such way, you can reuse, extend or modify the attributes and behaviors which are defined in other class.
In C++, the class which inherits the members of another class is called derived class and the class whose members are inherited is called base class. The derived class is the specialized class for the base class.
Sub Class: The class that inherits properties from another class is called Sub class or Derived Class.
Super Class:The class whose properties are inherited by sub class is called Base Class or Super class.

Basic Syntax of Inheritance

class Subclass_name : access_mode Superclass_name  

While defining a subclass like this, the super class must be already defined or atleast declared before the subclass declaration.
Access Mode is used to specify, the mode in which the properties of superclass will be inherited into subclass, public, privtate or protected

Modes of Inheritance

1. Public mode: If we derive a sub class from a public base class. Then the public member of the base class will become public in the derived class and protected members of the base class will become protected in derived class. Private members of the base class will never get inherited in sub class.
2. Protected mode: If we derive a sub class from a Protected base class. Then both public member and protected members of the base class will become protected in derived class. Private members of the base class will never get inherited in sub class.
3. Private mode: If we derive a sub class from a Private base class. Then both public member and protected members of the base class will become Private in derived class. Private members of the base class will never get inherited in sub class.

Table showing all the Visibility Modes

	Derived Class	Derived Class	Derived Class
Base class	Public Mode	Private Mode	Protected Mode
Private	Not Inherited	Not Inherited	Not Inherited
Protected	Protected	Private	Protected
Public	Public	Private	Protected

Inheritance Visibility Mode

Depending on Access modifier used while inheritance, the availability of class members of Super class in the sub class changes. It can either be private, protected or public.

1) Public Inheritance

This is the most used inheritance mode. In this the protected member of super class becomes protected members of sub class and public becomes public.

class Subclass : public Superclass

2) Private Inheritance

In private mode, the protected and public members of super class become private members of derived class.

class Subclass : Superclass   // By default its private inheritance

3) Protected Inheritance

In protected mode, the public and protected members of Super class becomes protected members of Sub class.

class subclass : protected Superclass

Forms of Inheritance

• Single Inheritance
• Multiple Inheritance
• Hierarchical Inheritance
• Multilevel Inheritance
• Hybrid Inheritance (also known as Virtual Inheritance)

Single Inheritance: In single inheritance, a class is allowed to inherit from only one class. i.e. one sub class is inherited by one base class only.
Syntax:

class subclass_name : access_mode base_class  
{    //body of subclass  };  

/ C++ program to explain

// Single inheritance

#include <iostream>

using namespace std;

// base class

class Vehicle {

  public:

    Vehicle()

    {

      cout << "This is a Vehicle" << endl;

    }

};

// sub class derived from two base classes

class Car: public Vehicle{

};

// main function

int main()

{  

    // creating object of sub class will

    // invoke the constructor of base classes

    Car obj;

    return 0;

}

Output:

This is a vehicle

Multiple Inheritance: Multiple Inheritance is a feature of C++ where a class can inherit from more than 

one classes. i.e one sub class is inherited from more than one base classes.

Syntax:

class subclass_name : access_mode base_class1, access_mode base_class2, ....  {    //body of subclass  };

Here, the number of base classes will be separated by a comma (‘, ‘) and access mode for every base class must be specified.

/ C++ program to explain

// multiple inheritance

#include <iostream>

using namespace std;

// first base class

class Vehicle {

  public:

    Vehicle()

    {

      cout << "This is a Vehicle" << endl;

    }

};

// second base class

class FourWheeler {

  public:

    FourWheeler()

    {

      cout << "This is a 4 wheeler Vehicle" << endl;

    }

};

// sub class derived from two base classes

class Car: public Vehicle, public FourWheeler {

};

// main function

int main()

{  

    // creating object of sub class will

    // invoke the constructor of base classes

    Car obj;

    return 0;

}

Output:

This is a Vehicle  This is a 4 wheeler Vehicle  

Multilevel Inheritance: In this type of inheritance, a derived class is created from another derived class.

// C++ program to implement

// Multilevel Inheritance

#include <iostream>

using namespace std;

// base class

class Vehicle

{

  public:

    Vehicle()

    {

      cout << "This is a Vehicle" << endl;

    }

};

class fourWheeler: public Vehicle

{  public:

    fourWheeler()

    {

      cout<<"Objects with 4 wheels are vehicles"<<endl;

    }

};

// sub class derived from two base classes

class Car: public fourWheeler{

   public:

     car()

     {

       cout<<"Car has 4 Wheels"<<endl;

     }

};

// main function

int main()

{  

    //creating object of sub class will

    //invoke the constructor of base classes

    Car obj;

    return 0;

}

output:

This is a Vehicle  
Objects with 4 wheels are vehicles  
Car has 4 Wheels

Hierarchical Inheritance: In this type of inheritance, more than one sub class is inherited from a single

 base class. i.e. more than one derived class is created from a single base class.

// C++ program to implement

// Hierarchical Inheritance

#include <iostream>

using namespace std;

// base class

class Vehicle

{

  public:

    Vehicle()

    {

      cout << "This is a Vehicle" << endl;

    }

};

// first sub class

class Car: public Vehicle

{

};

// second sub class

class Bus: public Vehicle

{

     

};

// main function

int main()

{  

    // creating object of sub class will

    // invoke the constructor of base class

    Car obj1;

    Bus obj2;

    return 0;

}

Output:

This is a Vehicle  This is a Vehicle

Hybrid (Virtual) Inheritance: Hybrid Inheritance is implemented by combining more than one type of inheritance. For example: Combining Hierarchical inheritance and Multiple Inheritance.
Below image shows the combination of hierarchical and multiple inheritance:

// C++ program for Hybrid Inheritance

#include <iostream>

using namespace std;

// base class

class Vehicle

{

  public:

    Vehicle()

    {

      cout << "This is a Vehicle" << endl;

    }

};

//base class

class Fare

{

    public:

    Fare()

    {

        cout<<"Fare of Vehicle\n";

    }

};

// first sub class

class Car: public Vehicle

{

};

// second sub class

class Bus: public Vehicle, public Fare

{

     

};

// main function

int main()

{  

    // creating object of sub class will

    // invoke the constructor of base class

    Bus obj2;

    return 0;

}

Output:

This is a Vehicle  
Fare of Vehicle