Virtual Functions

VIRTUAL FUNCTIONS:

If there are member functions with same name in base class and derived class, virtual functions gives programmer capability to call member function of different class by a same function call depending upon different context. This feature in C++ programming is known as polymorphism which is one of the important features of OOP.

If a base class and derived class has same function and if you write code to access that function using pointer of base class then, the function in the base class is executed even if, the object of derived class is referenced with that pointer variable.

Example:

#include <iostream.h>

class CPolygon

{

public:

int width, height;

void set_values (int a, int b)

{

width=a; height=b;

}

virtual int area ( )

{

Cout<<”Base Class Area of CPolygon”;

};

class CRectangle: public CPolygon

{

public:

int area (void)

{

return (width * height);

}

};

class CTriangle: public CPolygon

{

public:

int area ( )

{

return (width * height / 2);

}

};

void main ()

{

CRectangle rect;

CTriangle trgl;

CPolygon * ppoly1 = &rect;

CPolygon * ppoly2 = &trgl; ppoly1->set_values (4,5);

 ppoly2->set_values (4,5);

cout << ppoly1->area( ) << endl;

cout << ppoly2->area( ) << endl;

}

Output:

20

10

In this example class CPolygon includes a virtual function area( ). In this function we included the cout statement. When the base class pointer have derived class object and if the pointer points the function area() then the base class area() function is overloaded with the derived class function area().