Compile Time Polymorphism in C++

Last Updated on March 20, 2023 by Prepbytes

C++ programming language has a mechanism known as compile time polymorphism, also referred to as static polymorphism or early binding, that enables the choice of the appropriate method or function to be made at compile time.

What is Polymorphism in C++?

An important aspect of object-oriented programming is polymorphism, which makes it possible to treat objects of different classes as though they were objects of the same class by using virtual functions and inheritance. In other words, multiple forms are referred to as polymorphism.

A real-life example of polymorphism is the concept of a "vehicle". A vehicle can be a car, a truck, a motorcycle, or any other mode of transportation. Each type of vehicle has its own unique characteristics and behavior, but they all share certain common traits, such as the ability to move from one place to another.

There are mainly two types of polymorphism:

• Compile Time Polymorphism in C++: Compile time polymorphism in C++ is invoked during the compile time of the program. There are two ways to achieve compile-time polymorphism in C++:

  • Function Overloading
  • Operator Overloading

• Run Time Polymorphism in C++: Run time polymorphism in C++ is invoked during the run time of the program. There is one way to achieve the run time polymorphism in C++:

  • Function Overriding

What is Compile Time Polymorphism in C++?

The compile time polymorphism in C++ is a type of polymorphism, which refers to the ability of a programming language to determine the appropriate method or function to call at compile time-based on the types of arguments being passed.

There are a couple of ways to achieve compile time polymorphism in C++.

1. Function Overloading:

The C++ language’s function overloading feature enables us to define multiple functions that have the same name but different parameters. When we want to perform the same operation on various data types, or when we want to offer different levels of functionality depending on the quantity or kind of arguments passed, this can be helpful.

In C++, we simply define two or more functions with the same name but different parameters to overload a function. The compiler chooses which version of the function to call based on the number, type, and ordering of the arguments passed.

Let’s take an example to understand the compile time polymorphism in C++ using the function overloading.

// compile time polymorphism in C++
#include <iostream>
#include <bits/stdc++.h>

using namespace std;
class PrepBytes {
public:

    // Function with 1 int parameter
    void add(int x,int y)
    {
        std::cout << "The Sum of "<< x <<" and "<<y <<" is: " << x+y<<"\n";
    }

    // Function with same name but
    // 1 double parameter
    void add(int x, int y, int z)
    {
        std::cout << "The Sum of "<< x <<", "<< y <<" and "<<z <<" is: " << x+y+z << "\n";
    }

    // Function with same name and
    // 2 int parameters
    void add(double x, double y)
    {
        std::cout << "The Sum of "<< x <<" and "<<y <<" is: " << x+y<< "\n";
    }
    
    void add(double x, double y, double z)
    {
        std::cout << "The Sum of "<< x << ", " << y <<" and "<< z <<" is: " << x+y+z<< "\n";
    }
    
};

int main()
{
    PrepBytes obj;

    obj.add(7,8);
    obj.add(10,14,16);
    obj.add(4.5, 6.2);
    obj.add(1.3, 4.6, 7.2);
    
    return 0;
}

Output:

The Sum of 7 and 8 is: 15
The Sum of 10, 14 and 16 is: 40
The Sum of 4.5 and 6.2 is: 10.7
The Sum of 1.3, 4.6 and 7.2 is: 13.1

In the above C++ program, the class Prepbytes contains several methods with the same name add. During compile time, it will be decided which method to call based on the given arguments in the function parameter. For example, if we give 3 int data type arguments in the add function then it will call the second add function.

2. Operator Overloading:

In C++, a feature called operator overloading enables operators like +, -, *, /, and others to be redefined for user-defined data types. As a result, we can specify what the operator does when used with objects belonging to our own class, which enables us to write more logical and expressive code.

In C++, we define a function that starts with the operator keyword and the symbol we want to overload. For instance, we might define a function with the following signature to overload the addition operator + for the class "MyClass":

MyClass operator+(const MyClass& obj) const;

The ampersand (&) indicates that the function takes its argument by reference rather than by value and the keyword "const" indicates that it does not modify the object it is called on.

Let’s take an example to understand the compile time polymorphism in C++ using operator overloading.

// compile time ploymorphism in C++
#include <iostream>
using namespace std;

class Complex {
public:
    Complex(double r = 0.0, double i = 0.0) : real(r), imag(i) {}
    Complex operator+(const Complex& obj) const {
        return Complex(real + obj.real, imag + obj.imag);
    }
    void display() const {
        cout << real << " + " << imag << "i" << endl;
    }
private:
    double real, imag;
};

int main() {
    Complex c1(1.0, 2.0), c2(2.0, 3.0);
    Complex c3 = c1 + c2; // calls the overloaded + operator
    c3.display(); 
    return 0;
}

Output:

3 + 5i

In this example, we define a class called "Complex" that represents complex numbers with a real and imaginary components. We overload the addition operator (+) by defining a method called "operator+" that takes a Complex object as a reference and returns a new Complex object representing the sum of the two Complex objects.

Conclusion
In conclusion, this article will help you to understand what is polymorphism and types of the polymorphism. In addition, you will also learn how to achieve compile time polymorphism in C++ with help of an example.

FAQs of compile time polymorphism in C++

1. What are the advantages of compile-time polymorphism?
Compile-time polymorphism can help you write cleaner, more efficient code by allowing you to reuse function names and reduce redundancy. It also helps catch errors at compile time instead of at runtime, which can save you time and effort in debugging.

2. How does the compiler decide which version of an overloaded function to call?
The compiler decides which version of an overloaded function to call based on the number and types of arguments passed to it. It looks for the function with the best match for the arguments based on the standard conversion sequences defined in the C++ standard. If no exact match is found, it will try to find the best match through argument promotions, conversions, and user-defined conversions.

3. Can you overload constructors in C++ to achieve compile-time polymorphism?
Yes, you can overload constructors in C++ to achieve compile-time polymorphism. This allows you to create objects of the same class using different combinations of arguments, which can be useful in situations where you want to customize the behavior of an object based on its initialization.

4. Can you achieve compile-time polymorphism using inheritance in C++?
Yes, you can achieve compile-time polymorphism using inheritance in C++. This is often done through virtual functions and pure virtual functions, which allow you to define a common interface for a set of related classes.

5. What are the different ways to achieve compile time polymorphism in C++?
The two main ways to achieve compile time polymorphism in C++ are function overloading and operator overloading. Function overloading allows you to write multiple functions with the same name but different parameter lists, while operator overloading enables operators like +, -, *, /, and others to be redefined for user-defined data types.