Virtual functions allow functions to be overridden in derived classes. The virtual keyword before a function in the base class specifies that the function can be overridden. When a virtual function is called using a base class pointer, the version from the most derived class will be executed due to late binding. This allows runtime polymorphism where the function call is resolved based on the actual object type rather than the pointer variable type.

1. VIRTUAL FUNCTION
PRESENTED BY
Ms. V.VENNILA., MCA.,M.Phil.,
Asst.Prof of Information Technology,
Bon Secours College for Women,
Thanjavur

2. C++ VIRTUAL FUNCTION
Virtual function is a function in base class which
is overrided in the derived class , and which
tells the compiler to perform late binding on this
function.
Virtual keyword is used to make a member
function of the base class virtual,

3. VIRTUAL FUNCTION
A virtual function is a member function that is
declared as virtual within a base class and
redefined by a deriver class.
To create virtual function, precede the base
version of function’s declare with the keyword
virtual.
The method name and type signature should
be same for both base and derived version of
function.

4. Base class pointer can point to derived class object.
In this case, using base class pointer if we call
some function which is in both classes, then base
class function is invoked.
But if we want to invoke derived class function
using function base class pointer, it can be
achieved by defining the function as virtual in base
class, this is how virtual function supports runtime
polymorphism.
HOW VIRTUAL FUNCTION WORKS?

5. Using virtual keyword with base class version of
show function ; late binding takes place and
derived of the function will be called , because
base pointer pointes an derived type of object.
We know that in runtime polymorphism the call to
a function is resolved at runtime depending upon
the type of object.
USING VIRTUAL KEYWORD

6. Virtual return _ type function _ name ( )
{
……
……
……
}
Ex: virtual void print( )
SYNTAX

7. Class class _ name
{
Public:
virtual return _ type function _ name (arguments)
{
….
…..
}
};
Class A
{
GENDRAL FORMAT

8. Virtual function belongs to the branch of
runtime polymorphism in c++
polymorphism
Compile time/early binding Run time/late binding
Function
overloading
Operator
overloading
VIRTUAL
function/function
overloading

9. #include<iostream.h>
Class base
{
Public:
Virtual void print ( )
{
Cout<<“print base class”;
}
Void show ( )
{
Cout<<“show base class”;
} };
Class derived : public base
{
Public:
Void print ( )
{
Cout<<“print derived class”;
}
Void show ( )
EXAMPLE

10. {
cout<<“show derived class”;
}};
int main ( )
{
base*bptr;
bptr =d;
derived d;
bptr print( );
bptr show( );
}
OUTPUT
Print derived class
Show base class