Polymorphism in C++

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. Like 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 as one of the important features of Object-Oriented Programming. In C++, polymorphism is mainly divided into two types:

• Compile-time Polymorphism
• Runtime Polymorphism

Types of Polymorphism

1. Compile-time polymorphism: This type of polymorphism is achieved by function overloading or operator overloading.

• Function Overloading: When there are multiple functions with the same name but different parameters, then the functions are said to be overloaded. Functions can be overloaded by changing the number of arguments or/and changing the type of arguments. Rules of Function Overloading

CPP

// C++ program for function overloading
#include <bits/stdc++.h>

using namespace std;
class Geeks
{
    public:

    // function with 1 int parameter
    void func(int x)
    {
        cout << "value of x is " << x << endl;
    }

    // function with same name but 1 double parameter
    void func(double x)
    {
        cout << "value of x is " << x << endl;
    }

    // function with same name and 2 int parameters
    void func(int x, int y)
    {
        cout << "value of x and y is " << x << ", " << y << endl;
    }
};

int main() {

    Geeks obj1;

    // Which function is called will depend on the parameters passed
    // The first 'func' is called
    obj1.func(7);

    // The second 'func' is called
    obj1.func(9.132);

    // The third 'func' is called
    obj1.func(85,64);
    return 0;
}

• Output:

value of x is 7
value of x is 9.132
value of x and y is 85, 64

• In the above example, a single function named func acts differently in three different situations, which is a property of polymorphism.
• Operator Overloading: C++ also provides the option to overload operators. For example, we can make use of the addition operator (+) for string class to concatenate two strings. We know that the task of this operator is to add two operands. So a single operator ‘+’, when placed between integer operands, adds them and when placed between string operands, concatenates them. Example: 

CPP

// CPP program to illustrate
// Operator Overloading
#include<iostream>
using namespace std;

class Complex {
private:
    int real, imag;
public:
    Complex(int r = 0, int i =0)  {real = r;   imag = i;}

    // This is automatically called when '+' is used with
    // between two Complex objects
    Complex operator + (Complex const &obj) {
         Complex res;
         res.real = real + obj.real;
         res.imag = imag + obj.imag;
         return res;
    }
    void print() { cout << real << " + i" << imag << endl; }
};

int main()
{
    Complex c1(10, 5), c2(2, 4);
    Complex c3 = c1 + c2; // An example call to "operator+"
    c3.print();
}

• Output:

12 + i9

• In the above example, the operator ‘+’ is overloaded. Usually, this operator is used to add two numbers (integers or floating point numbers), but here the operator is made to perform the addition of two imaginary or complex numbers. To learn about operator overloading in detail, visit this link.

1. Runtime polymorphism: This type of polymorphism is achieved by 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. 

CPP

// C++ program for 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:
    void print () //print () is already virtual function in derived class, we could also declared as virtual void print () explicitly
    { cout<< "print derived class" <<endl; }

    void show ()
    { cout<< "show derived class" <<endl; }
};

//main function
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

• To learn about runtime polymorphism in detail, visit this link.

This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.