Inheritance and types of Inheritance in C++

Inheritance is a one of the most important feature of object oriented programming.

Inheritance allow an object of one class to acquire the properties of another object of another class.

It supports the reusability and support hierarchical classification.

The class which inherits the another class is called derived class and the class which inherited is called base class.

Syntax of creating a derived class:

class derived_class_name: access_specifier base_class_name {}

1	class derived_class_name: access_specifier base_class_name {}

Example:

 class B : public A	// public derivation								{										}

1	class B : public A // public derivation { }

In the above syntax, class A is a base class, class B is a derived class. Here class B is derived publicly.

Example:

class B : private A	// private derivation								{										}

1	class B : private A // private derivation { }

In the above syntax, class A is a base class, class B is a derived class.

Here class B is derived privately.

Example:

class B :  A	// by default private derivation								{										}

1	class B : A // by default private derivation { }

If no access specifier is given , by default derivation is private.

Public & Private Inheritance: In a C++ when a class derived and public access specifier is used.

All the public member of base class can be accessed directly in the derived class but when private access specifier is used, then even public member of base class can not access directly in derived class

Public Inheritance: When a public access specifier is used, the public member of the base class are the public member of the derived class.

Example:

#include <iostream>
using namespace std;
class A { //   Base class							
    public: int x;
};
class B: public A { //   Derived class 
    public: int y;void show() {
        x = 10;
        y = 20; // x is also public member of derived class B	
        cout << x << "  " << y;
    }
};
int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

public: int x;

};

class B: public A { // Derived class

public: int y;void show() {

x = 10;

y = 20; // x is also public member of derived class B

cout << x << " " << y;

}

};

int main() {

B obj;

obj.show();

}

Output

10 20

10 20

Description: In the above program, class B derives class A means class A is a base class, class B is a derived class.

During inheriting a class public access specifier is used therefore public member of base class A can directly access in derived class B.

In above program “x” is a public member of base class A but it can directly access in derived class B.

Private Inheritance: When a class derived and private access specifier is used, then an object of derived class has no permission to access even public member of base class directly in main() function.

In such case, the public member of base class can be accessed using public member function of the derived class.

Example : When a class derived and private access specifier is used, then an object of derived class has no permission to access even public member of base class directly in main() function.

#include <iostream>
using namespace std;
class A { //   Base class
    public: int x;
};
class B: private A { //   Derived class
    public: int y;
};
int main() {
    B obj;
    obj.x = 10; // error, x is not accessible here because x is a private member of derived class
    obj.y = 20;
    cout << obj.x; // error, x is not accessible here because x is a private member of derived class
    cout << obj.y;
}

#include <iostream>

using namespace std;

class A { // Base class

public: int x;

};

class B: private A { // Derived class

public: int y;

};

int main() {

B obj;

obj.x = 10; // error, x is not accessible here because x is a private member of derived class

obj.y = 20;

cout << obj.x; // error, x is not accessible here because x is a private member of derived class

cout << obj.y;

}

Output

 obj.x = 10; // error, x is not accessible here because x is a private member of derived class
 cout << obj.x; // error, x is not accessible here because x is a private member of derived class

1 2	obj.x = 10; // error, x is not accessible here because x is a private member of derived class cout << obj.x; // error, x is not accessible here because x is a private member of derived class

Solution of such problem is that the public member of base class can be accessed using public member function of the derived class.

#include <iostream>
using namespace std;
class A { //   Base class
    public: int x;
};
class B: private A { //   Derived class  
    public: int y;
    void show() {
        x = 10;
        y = 20; // x is private member of derived class & accessible here		
        cout << x << "  " << y;
    }
};
int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

public: int x;

};

class B: private A { // Derived class

public: int y;

void show() {

x = 10;

y = 20; // x is private member of derived class & accessible here

cout << x << " " << y;

}

};

int main() {

B obj;

obj.show();

}

Output

10  20

10 20

Derived class can not access private data of base class

In a C++ programming ,derived class can’t access private data of base class.

If we will try to do so we will get an error message.

Example: In the below program we are trying to access the private data of base class in a derived class.

#include <iostream>
using namespace std;
class A { //   Base class
    private: int x;
};
class B: public A { //   Derived class  
    public: int y;
    void show() {
        x = 10;
        y = 20; //error, x is private member of derived class		
        cout << x << "  " << y; //error, x is private member of derived class
    }
};
int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

private: int x;

};

class B: public A { // Derived class

public: int y;

void show() {

x = 10;

y = 20; //error, x is private member of derived class

cout << x << " " << y; //error, x is private member of derived class

}

};

int main() {

B obj;

obj.show();

}

Output

 error: ‘int A::x’ is private within this context
 cout << x << "  " << y; //error, x is private member of derived class

1 2	error: ‘int A::x’ is private within this context cout << x << " " << y; //error, x is private member of derived class

Protected access specifier with public derivation : when a protected access specifier is used, the protected member of the base class are the protected member of the derived class.

Protected access specifier : A protected access specifier is similar to the private only difference is that it has a access to their derived classes.

Example 1

#include <iostream>
using namespace std;
class A { //   Base class
    protected: int x;
};
class B: public A { //   Derived class
    public: void show() {
        x = 10; //x is accessible here because x is protected member of derived class	
        cout << x;
    }
};
int main() {
    B obj;
    obj.show();
}

#include <iostream>

using namespace std;

class A { // Base class

protected: int x;

};

class B: public A { // Derived class

public: void show() {

x = 10; //x is accessible here because x is protected member of derived class

cout << x;

}

};

int main() {

B obj;

obj.show();

}

Output

10

Example 2

#include <iostream>
using namespace std;
class A { //   Base class
    protected: int x;
};
class B: public A { //   Derived class  
    protected: int y;
};
int main() {
    B obj;
    obj.x = 10; // error, x is not accessible here because x is a protected member of derived class                       
    obj.y = 20; //error	
    cout << obj.x << " " << obj.y; //error
    return 0;
}

#include <iostream>

using namespace std;

class A { // Base class

protected: int x;

};

class B: public A { // Derived class

protected: int y;

};

int main() {

B obj;

obj.x = 10; // error, x is not accessible here because x is a protected member of derived class

obj.y = 20; //error

cout << obj.x << " " << obj.y; //error

return 0;

}

Output

error: ‘int A::x’ is protected within this context
    obj.x = 10; // error, x is not accessible here because x is a protected member of derived class

1 2	error: ‘int A::x’ is protected within this context obj.x = 10; // error, x is not accessible here because x is a protected member of derived class

Types of Inheritance

There are following types of inheritance supported by C++:

Single Inheritance
Multilevel Inheritance
Multiple Inheritance
Hierarchical Inheritance
Hybrid Inheritance
Multipath Inheritance

Single inheritance: When only one class derived a class and derived class is not used as a base class such type of inheritance are called Single inheritance.

Here, X is a base class, Y is a derived class. In a single inheritance there is only one base class and one derived class.

Multilevel Inheritance When a class derived from another derived class such type of inheritance is called multilevel inheritance.

Here X is s base class for Y, Y is a derived class from X and Y is also base class for Z. Z is a derived class from Y.

Multiple Inheritance : When a single class is derived from two or more then two class then such type of inheritance is called multiple inheritance.

X & Y are the base class for Z , Z is deriver class. Class Z is derived from Class X & Y.

Hierarchical Inheritance: When a two or more classes are derived from a single base class is known as hierarchical inheritance.

W is a only base class and X,Y & Z are derived class. X,Y & Z are the derived from W.

Hybrid Inheritance : The combination of two or more inheritance are called hybrid inheritance.

In this type two types of inheritance are use single inheritance and multilevel inheritance.

Single Inheritance: W is a base class, Z is a derived class. Single inheritance has only one base class and one derived class.

Multilevel Inheritance:X is s base class for Y, Y is a derived class from X and base class for Z. Z is a derived class from Y.

Multipath Inheritance : When a class derived from two or more classes that are derived from same base class such type of inheritance is known as multipath inheritance.

W is a base class and X & Y are derived class. The class X & Y are the derived from W.

Further Z is derived from X & Y. means X & Y is a base class for Z and Z is a derived class.

Here, ambiguity is generated. Hence, virtual keyword is used to avoid ambiguity.

Single Inheritance

Single inheritance: When only one class derived a class and derived class is not used as a base class such type of inheritance are called Single inheritance.

Here, X is a base class, Y is a derived class. In a single inheritance there is only one base class and one derived class.

Example: Write a program to create a base class student and derived class record to read student record such as name, roll number, age & height and display by using single inheritance.

#include <iostream>
using namespace std;
class student { // base class
    protected:
        char name[20];
    int rollno;
};
class record: public student { // derived class
    public: float height;
    int age;
    void getdata() {
        cout << " Enter Name, Roll number, Height & Age";
        cin >> name >> rollno >> height >> age;
    }
    void showdata() {
        cout << "Name= " << name << endl;
        cout << "Roll number =" << rollno << endl;
        cout << "Height=" << height << endl;
        cout << "Age =" << age << endl;
    }
};
int main() {
    record obj;
    obj.getdata();
    obj.showdata();
}

#include <iostream>

using namespace std;

class student { // base class

protected:

char name[20];

int rollno;

};

class record: public student { // derived class

public: float height;

int age;

void getdata() {

cout << " Enter Name, Roll number, Height & Age";

cin >> name >> rollno >> height >> age;

}

void showdata() {

cout << "Name= " << name << endl;

cout << "Roll number =" << rollno << endl;

cout << "Height=" << height << endl;

cout << "Age =" << age << endl;

}

};

int main() {

record obj;

obj.getdata();

obj.showdata();

}

Output

 Enter Name, Roll number, Height & Age 
Ram
2 
5.6
22

Name= Ram
Roll number =2
Height=5.6
Age =22

Enter Name, Roll number, Height & Age

Ram

5.6

Name= Ram

Roll number =2

Height=5.6

Age =22

Note: In the above program, we have created base class student and derived class record.

Student class holds the protected data member name & rollno(A protected data member is similar to the private only difference is that it has a access to their derived classes).

Class record is derived from student means that it inherits all properties of student class.

Multilevel Inheritance :When a class derived from another derived class such type of inheritance is called multilevel inheritance.

Here X is s base class for Y, Y is a derived class from X and Y is also base class for Z. Z is a derived class from Y.

Example: Write a program to read student record such as name, roll number & age and display by using the concept of multilevel inheritance, create classes A1, A2 & A3.

#include <iostream>
using namespace std;
class A1 { // base class		
  protected: char name[20];
};
class A2: public A1 { // base class for A3 & derives class from A1	
  protected: int rollno;
};
class A3: public A2 { // derived class from A2
  protected: int age;
  public:
  void getdata() {
    cout << "Enter name, roll number & age";
    cin >> name >> rollno >> age;
  }
  void showdata() {
    cout << "name = " << name << endl;
    cout << "roll number = " << rollno << endl;
    cout << "age = " << age << endl;
  }
};
int main() {
  A3 obj;
  obj.getdata();
  obj.showdata();
  return 0;
}

#include <iostream>

using namespace std;

class A1 { // base class

protected: char name[20];

};

class A2: public A1 { // base class for A3 & derives class from A1

protected: int rollno;

};

class A3: public A2 { // derived class from A2

protected: int age;

public:

void getdata() {

cout << "Enter name, roll number & age";

cin >> name >> rollno >> age;

}

void showdata() {

cout << "name = " << name << endl;

cout << "roll number = " << rollno << endl;

cout << "age = " << age << endl;

}

};

int main() {

A3 obj;

obj.getdata();

obj.showdata();

return 0;

}

Output

Enter name, roll number & age
name = Ram
roll number = 2
age = 23

Enter name, roll number & age

name = Ram

roll number = 2

age = 23

Multiple Inheritance : When a single class is derived from two or more then two class then such type of inheritance is called multiple inheritance

X & Y are the base class for Z , Z is deriver class. Class Z is derived from Class X & Y.

Example: Write a program to derive a class from multiple base classes.

#include <iostream>
using namespace std;
class A { // base class									
  public: int a;
};
class B { // base class	
  public: int b;
};
class C { // base class						
  public: int c;
};
class D: public A, public B, public C { // derived class D
  public: int d;void getdata() {
    cout << " Enter values of a, b, c, d ";
    cin >> a >> b >> c >> d;
  }
  void showdata() {
    cout << "Values of a, b, c, d = " << a <<" " << b<<" " << c<<"  "<< d;
  }
};
int main() {
  D obj;
  obj.getdata();
  obj.showdata();
  return 0;
}

#include <iostream>

using namespace std;

class A { // base class

public: int a;

};

class B { // base class

public: int b;

};

class C { // base class

public: int c;

};

class D: public A, public B, public C { // derived class D

public: int d;void getdata() {

cout << " Enter values of a, b, c, d ";

cin >> a >> b >> c >> d;

}

void showdata() {

cout << "Values of a, b, c, d = " << a <<" " << b<<" " << c<<" "<< d;

}

};

int main() {

D obj;

obj.getdata();

obj.showdata();

return 0;

}

Output

  Enter values of a, b, c, d
  10	// enter by user	
  20	// enter by user
  30	// enter by user
  40	// enter by user	 
  Values of a, b, c, d= 10  20  30  40

Enter values of a, b, c, d

10 // enter by user

20 // enter by user

30 // enter by user

40 // enter by user

Values of a, b, c, d= 10 20 30 40

Note: In this program, A, B & C are the base class and class D is derived class from A ,B & C .

Class D inherits the properties of class A, B & C.

Hierarchical Inheritance: When a two or more classes are derived from a single base class is known as hierarchical inheritance

W is a only base class and X,Y & Z are derived class. X,Y & Z are the derived from W.

Example: Write a program to show the hierarchical inheritance.

#include <iostream>
using namespace std;
class A { // base class A					
  public: int a;
};
class B: public A { // derived class	B from class A
  public: int b;
  void showB() {
    a = 10;
    b = 20;
    cout << "a + b = " << (a + b)<<endl;
  }
};
class C: public A { // derived class	C  from class A	
  public: int c;
  void showC() {
    a = 10;
    c = 30;
    cout << "a + c = " << (a + c)<<endl;
  }
};
class D: public A { // derived class	D  from class A	
  public: int d;
  void showD() {
    a = 10;
    d = 40;
    cout << "a + d = " << (a + d)<<endl;
  }
};
int main() {
  B ob1;
  C ob2;
  D ob3;
  ob1.showB();
  ob2.showC();
  ob3.showD();
  return 0;
}

#include <iostream>

using namespace std;

class A { // base class A

public: int a;

};

class B: public A { // derived class B from class A

public: int b;

void showB() {

a = 10;

b = 20;

cout << "a + b = " << (a + b)<<endl;

}

};

class C: public A { // derived class C from class A

public: int c;

void showC() {

a = 10;

c = 30;

cout << "a + c = " << (a + c)<<endl;

}

};

class D: public A { // derived class D from class A

public: int d;

void showD() {

a = 10;

d = 40;

cout << "a + d = " << (a + d)<<endl;

}

};

int main() {

B ob1;

C ob2;

D ob3;

ob1.showB();

ob2.showC();

ob3.showD();

return 0;

}

Output

a + b = 30
a + c = 40
a + d = 50

a + b = 30

a + c = 40

a + d = 50

Note: A is a only base class. B, C & D are the derived class from A. Class B,C & D all inherits the properties of class A.

Hybrid Inheritance : The combination of two or more inheritance are called hybrid inheritance.

In this type two types of inheritance are use single inheritance and multilevel inheritance.

Single Inheritance: W is a base class, Z is a derived class. Single inheritance has only one base class and one derived class.

Multilevel Inheritance: X is s base class for Y, Y is a derived class from X and base class for Z. Z is a derived class from Y.

Example: Write a program to show the hybrid inheritance.

Write a program to create a derived class from multiple base class.

Write a program to create hybrid inheritance and take data members such as name of the player, age, city and game name.

#include <iostream>
using namespace std;
class location { // base class  
  public: char city[20];
};
class player { // base class	
  public: char name[20];
};
class year: public player { //   derived class from player & base class for game  
  public: int age;
};
class game: public year, public location { //  derived class from player & location.
  public: char game_name[20];
  void getdata() {
    cout << "Enter name, age, city & game name";
    cin >> name >> age >> city >> game_name;
  }
  void showdata() {
    cout << "name = " << name << endl;
    cout << "age = " << age << endl;
    cout << "city = " << city << endl;
    cout << "game name = " << game_name << endl;
  }
};
int main() {
  game ob;
  ob.getdata();
  ob.showdata();
}

#include <iostream>

using namespace std;

class location { // base class

public: char city[20];

};

class player { // base class

public: char name[20];

};

class year: public player { // derived class from player & base class for game

public: int age;

};

class game: public year, public location { // derived class from player & location.

public: char game_name[20];

void getdata() {

cout << "Enter name, age, city & game name";

cin >> name >> age >> city >> game_name;

}

void showdata() {

cout << "name = " << name << endl;

cout << "age = " << age << endl;

cout << "city = " << city << endl;

cout << "game name = " << game_name << endl;

}

};

int main() {

game ob;

ob.getdata();

ob.showdata();

}

Output

Enter name, age, city & game name
name = Ram
age = 23
city = Bhopal
game name = Chess

Enter name, age, city & game name

name = Ram

age = 23

city = Bhopal

game name = Chess

Note: In this type two types of inheritance are used single inheritance and multilevel inheritance.

Single Inheritance: location is a base class, game is a derived class.

Single level inheritance has only one base class and one derived class.

Class game inherits the properties of class location.

Multilevel Inheritance: player is a base class for Year, Year is a derived class from player .

year is a base class for game. game is a derived class from Year. Class game inherits the properties of both class player & year.

Multipath Inheritance : When a class derived from two or more classes that are derived from same base class such type of inheritance is known as multipath inheritance.

W is a base class and X & Y are derived class. The class X & Y are the derived from W. Further Z is derived from X & Y.

Means X & Y is a base class for Z and Z is a derived class. Here, ambiguity is generated.

Hence, virtual keyword is used to avoid ambiguity.

Example:

class A1 {
  protected: int a1;
};
class A2: public A1 {
  protected: int a2;
};
class A3: public A1 {
  protected: int a3;
};
class A4: public A2, public A3 {
  protected: int a4;
};

class A1 {

protected: int a1;

};

class A2: public A1 {

protected: int a2;

};

class A3: public A1 {

protected: int a3;

};

class A4: public A2, public A3 {

protected: int a4;

};

In the above example, A1 is a base class. The class A2 & A3 are the derived from class A1. Both A2 and A3 can access the variables/data of class A1 .

Further A4 is derived from A2 & A3.

If we try to access variable a1 of class A1 from class A4, Here, ambiguity is generated & compiler shows error message.

Member is ambiguous : “A1:a1” and “A1:a1”

The derived class A4 has two sets of data member of class A1 through the middle base classes A2 and A3.

The A1 is inherited twice.

Hence, virtual keyword is used to avoid ambiguity.