Understanding Polymorphism in C : Compile-Time and Run-Time Polymorphism Explained

Polymorphism is a fundamental concept in programming, particularly in Object-Oriented Programming (OOP). It allows objects to take on multiple forms, thus providing a powerful way to abstract and generalize functionality. In this article, we will delve deep into the concept of polymorphism, discussing its significance, and explaining how compile-time and run-time polymorphism are achieved in C .

What is Polymorphism?

Polymorphism, derived from the Greek words for many forms, means having many forms. In programming, it refers to the ability of a message to be displayed in more than one form. This concept is crucial in OOP as it allows objects with different internal structures to share the same external interface. It enhances the flexibility and reusability of code by allowing operations to perform different tasks based on the context in which they are used.

Operations and Their Role in Polymorphism

An operation, in the context of a class, is a function that can be applied to or by objects in that class. For example, let's consider a class Window. It has several operations such as open, close, hide, and redisplay. These operations are shared by all objects of the same class, and each operation carries an implicit target object. The behavior of these operations is determined by the class of the target object.

Compile-Time Polymorphism (C )

Compile-time polymorphism, also known as compile-time binding or static binding, is achieved using function overloading in C . In C , compile-time polymorphism is achieved when a single function name can perform various tasks, and the appropriate function to be called is determined at compile time based on the operand types. Let's illustrate this with an example.

Example: Function Overloading in C

Consider the following code:

class File { public: void print(int data); void print(string data); };

In this example, the print function is overloaded to accept different types of data. When the print function is called, the appropriate function is determined based on the type of the argument, which is decided at compile time.

Run-Time Polymorphism (C )

Run-time polymorphism, also known as late binding, is achieved using virtual functions in C . In this case, the appropriate function is determined at run time, based on the actual object type. Let's see how this works with an example.

Example: Run-Time Polymorphism with Virtual Functions

Consider the following code:

class Base { public: virtual void print()  0; }; class Derived : public Base { public: void print() override { cout Derived class print function; } }; void callPrint(Base* obj) { obj->print(); }

In this example, the callPrint function takes a pointer to the Base class and calls the print function. If the actual object is of type Derived, the Derived version of the print function is called, demonstrating run-time polymorphism.

Classifying Polymorphism: Ad-Hoc vs. Universal

There are two types of polymorphism in programming languages: ad-hoc and universal. Ad-hoc polymorphism is a type of polymorphism where a polymorphic function can be applied to arguments of different types, with the appropriate function being chosen at compile time. An example of ad-hoc polymorphism is C function overloading.

On the other hand, universal polymorphism involves the writing of polymorphic functions without reference to any specific type. C virtual functions are an example of universal polymorphism. Such polymorphism is primarily applicable to object-oriented systems.

Polymorphism for Newbies

Explaining polymorphism to newbies can be tricky, but a simple analogy might help. Polymorphism can be visualized as a car that can run on both fuel and solar energy, each with its unique way of converting energy. In the context of programming, a CarSystem class might inherit from both SolarEnergy and Fuel classes, allowing it to utilize the methods from both classes while handling them differently. Here is an example in C :

class SolarEnergy { public: void generateElectricity() {} }; class Fuel { public: void storeEnergy() {} }; class CarSystem : protected SolarEnergy, protected Fuel { public: CarSystem() : SolarEnergy(), Fuel() {} void start() { generateElectricity(); storeEnergy(); } }; int main() { CarSystem car; (); return 0; }

Similarly, a CarSystem might have a start function that utilizes methods from both SolarEnergy and Fuel classes. In this way, the object CarSystem can derive its functionality from different base classes, allowing for a more flexible and dynamic design.

Conclusion

Polymorphism is an invaluable concept in C and object-oriented programming in general. By enabling objects to take on multiple forms based on the context, polymorphism enhances the flexibility, reusability, and robustness of code. Whether through compile-time overloading or run-time virtual functions, understanding and implementing polymorphism is crucial for any C developer.