What are Virtual Functions?

What are Virtual Functions? How to use the virtual functions in C++?
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Virtual Functions are the basis of Polymorphism concept as they provide the mechanics of late binding. A class, which has at least one function declared as Virtual has a V-Table associated with it. V-Table maintains pointers of all the Virtual functions of that class. Virtual functions are marked using Virtual keyword.

All objects of that class point to the same V-Table. Whenever there is a call made to a function which is virtual, the pointer to that function is obtained during runtime from the V-Table. Hence there is dynamic binding or late binding that leads to the function of the derived class getting called.

Code Example:
cpp code

class Shape  
     {
       public:
          virtual void Draw() // virtual function for C++ virtual function example
          {
               cout <<"I am  class Shape";        
			     }
     };

     class Line : public Shape
     {
       public:
          void Draw()
          {
              cout<<"I am line class - Overridden   virtual function";        
			  }
     };

     void main()
     {
         Shape  *x, *y;
  
         x = new Shape();
         x->Draw();

         y = new Line();
         y->Draw();
     }

The output is :

Code:

I am  class Shape
I am line class - Overridden   virtual function

updated.