CPP Tutorial

Interfaces in C++

In C++, there is no direct interface keyword like in some other languages (e.g., Java or C#), but you can create an interface using an abstract class that contains only pure virtual functions.

An interface defines a contract that derived classes must follow by implementing all the pure virtual functions.

How to create an Interface in C++?

• Make a class with only pure virtual functions.
• No data members or implemented methods inside the interface.
• The class becomes abstract and cannot be instantiated.

Example of an Interface:

#include <iostream>
using namespace std;

// Interface declaration
class IAnimal {
  public:
    virtual void makeSound() = 0;  // Pure virtual function
    virtual void move() = 0;       // Pure virtual function
    virtual ~IAnimal() {}           // Virtual destructor for cleanup
};

class Dog : public IAnimal {
  public:
    void makeSound() override {
      cout << "Dog says: Woof Woof!" << endl;
    }
    void move() override {
      cout << "Dog runs" << endl;
    }
};

class Bird : public IAnimal {
  public:
    void makeSound() override {
      cout << "Bird says: Tweet Tweet!" << endl;
    }
    void move() override {
      cout << "Bird flies" << endl;
    }
};

int main() {
  IAnimal* animal1 = new Dog();
  IAnimal* animal2 = new Bird();

  animal1->makeSound();
  animal1->move();

  animal2->makeSound();
  animal2->move();

  delete animal1;
  delete animal2;

  return 0;
}
  

🖨️ Output:

Summary:

• Interfaces in C++ are abstract classes with only pure virtual functions.
• Derived classes must override all the pure virtual functions.
• Interfaces define a common behavior that different classes can implement.
• Use pointers or references to interface types for polymorphism.