Virtual Functions

Virtual Function is a function that is declared within a base class and redefined in the derived class. Virtual functions are declared by preceding the class declaration with a keyword "virtual". When a virtual function is declared C++ decides to execute a function based on the type of object pointed by the base pointer and not on the type of pointer.

Example :

#include <iostream.h> class Bclass { public: void disp() { cout << " BASE BASE\n" ; } virtual void sh() { cout << "base base\n"; } }; class Dclass : public Bclass { public: void disp() { cout << "DERIVED DERIVED\n"; } void sh() { cout << "derived derived\n"; } }; int main() { Bclass B; Dclass D; Bclass *ptr; cout << "ptr points to base class\n" ; ptr = &B; ptr->disp(); ptr->sh(); cout << "ptr points derived class\n"; ptr = &D; ptr->disp(); ptr->sh(); return 0; }

Result :
In the above example, the base ptr is used point the object D. Since the "sh()" function has a derived version in the form of a virtual function, it displays the base class version of "sh()".