What is Pure Virtual Function in C++?
What is Pure Virtual Function in C++?

In the ever-changing world of programming, we come across different elements of it helping programmers to enhance their craft. Today we’ll be looking at a what is pure virtual function in C++ which is a function declared in an abstract base class that has no implementation in the base class and is marked with the = 0 syntax. This concept plays a very crucial role as it stands as a foundation paving the way developers create and design the code. 

Picture this: there’s a tool which helps you to create accurate, extensible and functional software architecture for your projects sounds good right? pure virtual functions are precisely that tool. The pure virtual functions act as a placeholder in the system and any derived class must offer an implementation for the function. One pure virtual function in a class makes that class an abstract base class which eventually means it cannot be instantiated on its own. 

As we move forward we’ll understand unique and engaging elements of pure virtual functions in C++, exploring their importance, characteristics, advantages, disadvantages, and why every programmer needs to grasp their essence.

Opening The Gates To Code Modularity

Imagine you’re in the middle of crafting a sophisticated C++ program and out of the blue you encounter a situation where the base class in your program needs to be declared as a function that must be applied by its derived classes. Here comes the pure virtual functions which open the gates to code modularity and flexibility as they serve as a blueprint, demanding enactment from derived classes, and thus fostering a strong inheritance order. 

What is Pure Virtual Function in C++? with Example

Definition: A function declared in an abstract base without offering any enactment is called a pure virtual function in C++. This acts as a contract, stating that any derived class must use this function.

Unlike regular virtual functions, pure virtual functions lack a defined body, making it one of the most   powerful tools for enforcing structure and promoting a standardized approach to code implementation.

Pure Virtual Function in C++ Example

class Shape {


    virtual void draw() const = 0; // Pure virtual function


Use & Advantages of Pure Virtual Function in C++

    1.Abstraction and Polymorphism:

Pure virtual functions facilitate the creation of abstract base classes, enabling the encapsulation of common features shared among derived classes. This abstraction promotes polymorphism, allowing objects of different derived types to be manipulated through a common interface.

  1. Enforcing Contracts:

By declaring pure virtual functions in a base class, developers establish a contractual obligation for derived classes to implement specific behavior. This ensures consistency in the design and execution of derived classes.

  1. Modular Code Design:

The use of pure virtual functions encourages a modular approach to code design. Each derived class focuses on implementing its unique functionality, promoting separation of concerns and making the codebase more maintainable.

  1. Code Reusability:

Through the inheritance hierarchy established by pure virtual functions, developers can reuse and extend existing code. Derived classes inherit the structure and behavior of the base class, fostering a DRY (Don’t Repeat Yourself) programming philosophy.

Drawback of Pure Virtual Functions

  1. Inflexibility:

Once a pure virtual function is declared in a base class, all derived classes must implement it. This rigidity can be limiting in scenarios where certain derived classes may not need to provide an implementation for a particular function.

  1. Increased Complexity:

The use of pure virtual functions may introduce complexity to the codebase, especially in larger projects with intricate inheritance hierarchies. Understanding and navigating the relationships between classes becomes crucial for developers.

  1. Run-Time Overhead:

Imagine a fast food place with a Special Menu Pure virtual functions are like a special menu. They outline dishes (functions) that must be offered, but each chef (derived class) prepares them differently. The vtable is like a waiter: It knows which chef specializes in which dish and directs orders accordingly.

When you call a pure virtual function, it’s like a customer ordering from the special menu. The waiter (program) consults the vtable (like a kitchen staff list) to see which chef (derived class) specializes in that dish (the correct function implementation). The waiter relays the order to the appropriate chef, who then prepares the dish (executes the function) according to their unique recipe (implementation).

Pure virtual functions provide flexibility and adaptability through polymorphism.
The vtable mechanism enables this polymorphism but adds a small run-time overhead.

Why Every Programmer Should Know About Pure Virtual Functions

Object-Oriented Mastery

Understanding pure virtual functions is fundamental to mastering object-oriented programming in C++. It empowers developers to leverage the full potential of polymorphism and inheritance, two pillars of object-oriented design.

Design Patterns

Many design patterns, such as the Template Method Pattern and the Factory Method Pattern, rely on pure virtual functions to achieve flexibility and extensibility. Proficient knowledge of these patterns is invaluable for creating scalable and maintainable code.

Code Maintenance and Collaboration

In collaborative programming environments, adherence to standardized practices, such as the use of pure virtual functions, enhances code readability and maintainability. Team members can easily comprehend and extend the functionality of existing code.

Industry Relevance

Proficiency in C++ and its advanced features, including pure virtual functions, is highly valued in the software development industry. Employers seek developers who can design elegant and efficient solutions, and a solid grasp of pure virtual functions demonstrates this capability.

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Frequently asked Question’s 

What is the difference between pure and non-pure virtual?

A Pure virtual function has no implementation in base class, non-pure has both base and derived class implementations. Both allow runtime polymorphism.

What is the difference between virtual function and abstract function?

All abstract functions are virtual, but not all virtual functions are abstract. Abstract functions require at least one pure virtual function.

What is pure virtual function?

A function declared in an abstract base without offering any enactment is called a pure virtual function in C++.


In the grand symphony of C++ programming, pure virtual functions emerge as a key melody, harmonizing the intricate relationships between classes and unlocking the doors to code elegance. From abstraction and polymorphism to enforcing contracts and facilitating modular design, the advantages of pure virtual functions are manifold. Yet, as with any powerful tool, there are trade-offs, including inflexibility and potential complexity.

Every programmer aspiring for mastery in C++ should delve into the realm of pure virtual function in c++, know what is pure virtual function in c++ ? recognizing them not merely as syntax but as a gateway to a world where code becomes a flexible, scalable, and maintainable entity. In embracing the power of pure virtual functions, programmers embark on a journey to craft software that stands the test of time—a testament to the artistry and ingenuity inherent in the world of C++ development.