Single Inheritance – Public Inheritance in C++

Inheritance in which the derived class is derived from only one base class is calledsingle inheritance.

Let us consider a simple example to illustrate the single inheritance. Program given below shows a base class B and a derived class D. The class B contains one private data member, one public data member and three public member functions. The class D contains one private data member and two public member functions.

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#include<iostream.h>   class B    {       private:          int a;      //private; not inheritable       public:          int b;      //public; ready for inheritance          void get_ab();          int get_a();          void show_a();    };   class D : public B      //public derivation    {       private:          int c;       public:          void mul();          void display();    };   /*...Defining of functions...*/   void B :: get_ab()    {       a = 5;       b = 10;    }   int B :: get_a()    {       return a;    }   void B :: show_a()    {       cout << "a = " << a <<endl;    }   void D :: mul()    {       c = b * get_a();    }   void D :: display()    {       cout << "a = " << get_a() << endl;       cout << "b = " << b << endl;       cout << "c = " << c << endl;    }   /*...Main Program...*/   void main()    {       D x;          x.get_ab();       x.mul();       x.show_a();       x.display()         x.b = 20;       x.mul();       x.display();    }

Given below is the output of the above program:

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a = 5 a = 5 b = 10 c = 50   a = 5 b = 20 c = 100

In the above program, following things require to be noted:

1. The class D is a public derivation of the base class B. Therefore, class D inherits all the public members of class B an retains their visibility. Thus, a public member of the base class B is also a public member of the derived class D
2. The private members of the base class B cannot be inherited by the derived class D
3. The class D, in effect, will have more members than what it contains at the time of declaration
4. The program illustrates that the objects of class D have access to all the public members of class B

Let us have a look at the function show_a() and mul():

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void B :: show_a()    {       cout << "a = " << a <<endl;    }   void D :: mul()    {       c = b * get_a();    }

Although the data member a is a private member of base class B and cannot be inherited, objects of derived class D are able to access it through an inherited member function of class B.