OOPS - [C++ Virtual Function]

♠ Posted by Unknown in CPP Language at 04:07

Virtual Function

When we use the same function name in both the base and derived classes, the function in base class id declared as virtual using virtual preceding its normal declaration.
When a function is made virtual, C++ determines which function to use at run time base on the type of object pointed to by the bas pointer, rather than the type of the pointer. Thus, by making the base pointer to point to different objects, we can execute different versions of the virtual function.

Example:

#include<iostream.h>

#include<conio.h>

class Base

{

 public:

            void display()

            { cout<<"\nDisplay Base : "; }

            virtual void show()

            { cout<<"\nShow Base : "; }

};

class Derived : public Base

{

 public:

            void display()

            { cout<<"\nDisplay Derived : "; }

            void show()

            { cout<<"\nShow Derived : "; }

};

void main()

{

 Base B;

 Derived D;

 Base *bptr;

 cout<<"\nbptr points to Base \n";

 bptr = &B;

 bptr->display(); //calls Base Version

 bptr->show();  //Calls Base Version

 cout<<"\n\n bptr points to Derived\n";

 bptr = &D;

 bptr->display();  //Calls Base Version

 bptr->show();  //Calls Derived Version

}