Advantages of Pure Virtual Functions

Pure virtual functions have a few key use cases:

1. Enforce Interface Implementation

Pure virtual functions ensure that derived classes implement specific functions.

This enforces a contract, making it clear what functionality must be provided by any class that inherits from the base class.

2. Design Flexibility

They allow you to define a common interface for a set of classes without providing a specific implementation in the base class.

This gives derived classes the flexibility to implement the details.

3. Encapsulation of Common Functionality

Abstract classes can contain non-virtual functions that provide common functionality, while pure virtual functions define the interface.

This helps in keeping the shared code centralized and reduces duplication.

4. Polymorphism

Pure virtual functions enable polymorphic behavior, allowing you to write code that can operate on a base class reference or pointer but execute derived class methods.

Disadvantages of Pure Virtual Functions

1. Increased Complexity: They can increase the complexity of the class hierarchy. Managing multiple derived classes that implement various interfaces can become challenging.
2. Difficulty in Refactoring: Changing the interface of a pure virtual function requires changes in all derived classes, which can be cumbersome if there are many subclasses.
3. Cannot Instantiate Base Class: You cannot instantiate an abstract class, which might be limiting if you want to create objects of the base class directly for some reason.

Example

Here’s an example to illustrate the use of pure virtual functions:

1#include <iostream>
2#include <string>
3
4// Abstract base class with a pure virtual function
5class Animal {
6public:
7  virtual void MakeSound() = 0; 
8};
9
10class Dog : public Animal {
11public:
12  void MakeSound() override {
13    std::cout << "Bark!\n";
14  }
15};
16
17class Cat : public Animal {
18public:
19  void MakeSound() override {
20    std::cout << "Meow!\n";
21  }
22};
23
24int main() {
25  Dog dog;
26  Cat cat;
27
28  dog.MakeSound(); 
29  cat.MakeSound(); 
30}

1Bark!
2Meow!

In this example:

• Animal is an abstract class with a pure virtual function MakeSound().
• Dog and Cat provide implementations for the MakeSound() function, enforcing the contract.

Pure virtual functions are a powerful feature in C++ that help enforce design contracts, enable polymorphism, and provide design flexibility, despite their complexity.