Pure Virtual Function Necessity

Pure virtual functions are necessary when you want to define an interface that must be implemented by derived classes.

This is especially useful in designing frameworks or libraries where you want to ensure that certain functions are always implemented in the derived classes, providing specific behaviors.

For instance, imagine you are creating a game with different types of characters, and each character type must have a unique attack method.

You can define a pure virtual function in a base class Character to enforce this requirement:

1#include <iostream>
2#include <string>
3
4// Base class with a pure virtual function
5class Character {
6public:
7  virtual void Attack() = 0; 
8};
9
10class Warrior : public Character {
11public:
12  void Attack() override {
13    std::cout << "Warrior attacks with a sword!\n";
14  }
15};
16
17class Mage : public Character {
18public:
19  void Attack() override {
20    std::cout << "Mage casts a fireball!\n";
21  }
22};
23
24int main() {
25  Warrior warrior;
26  Mage mage;
27
28  warrior.Attack(); 
29  mage.Attack(); 
30}

1Warrior attacks with a sword!
2Mage casts a fireball!

In this example:

• Character has a pure virtual function Attack(). This means Character is an abstract class, and you cannot instantiate it directly.
• Warrior and Mage are derived classes that must provide an implementation of the Attack() function. Each class defines its unique attack behavior.

Using pure virtual functions ensures that every derived class implements the Attack() method, providing the required behavior.

This design is essential when you want to enforce a specific interface across different classes, ensuring they adhere to a common contract.