Runtime Polymorphism

1. Compile-Time Polymorphism

This type of polymorphism is achieved by Function Overriding. Late binding and dynamic polymorphism are other names for runtime polymorphism. The function call is resolved at runtime in runtime polymorphism. In contrast, with compile time polymorphism, the compiler determines which function call to bind to the object after deducing it at runtime.

A. Function Overriding

Function Overriding occurs when a derived class has a definition for one of the member functions of the base class. That base function is said to be overridden.

Function overriding Explanation

Runtime Polymorphism with Data Members

Runtime Polymorphism cannot be achieved by data members in C++. Let’s see an example where we are accessing the field by reference variable of parent class which refers to the instance of the derived class.

C++

// C++ program for function overriding with data members
#include <bits/stdc++.h>
using namespace std;
 
//  base class declaration.
class Animal {
public:
    string color = "Black";
};
 
// inheriting Animal class.
class Dog : public Animal {
public:
    string color = "Grey";
};
 
// Driver code
int main(void)
{
    Animal d = Dog(); // accessing the field by reference
                      // variable which refers to derived
    cout << d.color;
}

Output

Black

We can see that the parent class reference will always refer to the data member of the parent class.

B. Virtual Function

A virtual function is a member function that is declared in the base class using the keyword virtual and is re-defined (Overridden) in the derived class.

Some Key Points About Virtual Functions:

Virtual functions are Dynamic in nature.
They are defined by inserting the keyword “virtual” inside a base class and are always declared with a base class and overridden in a child class
A virtual function is called during Runtime

Below is the C++ program to demonstrate virtual function:

C++

// C++ Program to demonstrate
// the Virtual Function
#include <iostream>
using namespace std;
 
// Declaring a Base class
class GFG_Base {
 
public:
    // virtual function
    virtual void display()
    {
        cout << "Called virtual Base Class function"
             << "\n\n";
    }
 
    void print()
    {
        cout << "Called GFG_Base print function"
             << "\n\n";
    }
};
 
// Declaring a Child Class
class GFG_Child : public GFG_Base {
 
public:
    void display()
    {
        cout << "Called GFG_Child Display Function"
             << "\n\n";
    }
 
    void print()
    {
        cout << "Called GFG_Child print Function"
             << "\n\n";
    }
};
 
// Driver code
int main()
{
    // Create a reference of class GFG_Base
    GFG_Base* base;
 
    GFG_Child child;
 
    base = &child;
 
    // This will call the virtual function
    base->GFG_Base::display();
 
    // this will call the non-virtual function
    base->print();
}

Output

Called virtual Base Class function

Called GFG_Base print function

Example 2:

C++

// C++ program for virtual function overriding
#include <bits/stdc++.h>
using namespace std;
 
class base {
public:
    virtual void print()
    {
        cout << "print base class" << endl;
    }
 
    void show() { cout << "show base class" << endl; }
};
 
class derived : public base {
public:
    // print () is already virtual function in
    // derived class, we could also declared as
    // virtual void print () explicitly
    void print() { cout << "print derived class" << endl; }
 
    void show() { cout << "show derived class" << endl; }
};
 
// Driver code
int main()
{
    base* bptr;
    derived d;
    bptr = &d;
 
    // Virtual function, binded at
    // runtime (Runtime polymorphism)
    bptr->print();
 
    // Non-virtual function, binded
    // at compile time
    bptr->show();
 
    return 0;
}

Output

print derived class
show base class

C++ Polymorphism

The word “polymorphism” means having many forms. In simple words, we can define polymorphism as the ability of a message to be displayed in more than one form. A real-life example of polymorphism is a person who at the same time can have different characteristics. A man at the same time is a father, a husband, and an employee. So the same person exhibits different behavior in different situations. This is called polymorphism. Polymorphism is considered one of the important features of Object-Oriented Programming.

Tags:

#CPP-OOPs #C++ #CPP

1. Compile-Time Polymorphism

Runtime Polymorphism

A. Function Overriding

Runtime Polymorphism with Data Members

C++

B. Virtual Function

Some Key Points About Virtual Functions:

C++

C++

C++ Polymorphism

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