C++ – Dynamic Polymorphism

Hello Friends,

Today, in this article we will mostly discuss about Dynamic Polymorphism and the difference between Static Polymorphism and Dynamic Polymorphism .

Static Polymorphism : If function call binding is performed at compile time. This is also known as Compile time binding / Early binding. (Please refer to previous blog for details of Static Polymorphism :  C++ – Static Polymorphism  )

Dynamic Polymorphism : If function call binding is performed at run time. This is also known as Run-time binding / Late binding.

Purpose of Dynamic Polymorphism :

• We can store derived class object in a base class pointer .
• Assume that : same named function is available in base class as well as derived classes (which is called function overriding , achieved by declaring method as virtual ).
• If we store a derived class object in a base class pointer and call a particular function through the base class pointer , the expectation is : it should call the function which is  available in derived class (whose address is stored in base class pointer ) instead of calling the function which is available in base class . This is the goal of Dynamic polymorphism .

Let’s analyse the below program.

Sample code 1

class base
{
	public:
	void show()
	{
		cout<<"user in base class"<<endl;
	}
};

class derived:public base
{
	public:
	void show()
	{
		cout<<"user in derived class"<<endl; 
	} 
}; 

int main() 
{ 
    derived child; 
	base *p = new base;  /*Base class pointer which points to base class object*/ 
	p->show();        //Call base class show() method
	p = &child;     /*base class pointer stores the address of derived class object child*/
	p->show();       //Call base class show() method
	getchar();
	return 0;
}

O/P -> user in base class                                                                                                                    user in base class

As the ideal case , we will expect that after storing the derived class object in base class pointer , the show method call should call the derived class show method . But it didn’t happen .

Here the function binding happens at compile time . As the pointer is base type , compiler will bind the function call to base class “show()” method .

In this case to call the method of the actual stored object,  we have to declare the method as virtual which lead to late binding instead of compile time binding .

Note * -> We will discuss details of virtual keyword and how compiler internally handles this in next blog .

Program using virtual method:

class base
{
	public:
	virtual void show()
	{
		cout<<"user in base class"<<endl;
	}
};

class derived:public base
{
	public:
	void show() override
	{
		cout<<"user in derived class"<<endl; 
	} 
}; 

int main() 
{ 
	derived child; 
	base *p = new base; 
	p->show();
	p = &child;
	p->show();     //This will call derived class show() method
	getchar();

	return 0;
}

O/P -> user in base class                                                                                                                      user in derived class

Difference between Static Polymorphism & Dynamic Polymorphism

Thanks for reading 🙂

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