Polymorphism — C++ Tutorial

Virtual Functions and Abstract Classes

Runtime polymorphism in C++ is achieved through virtual functions. Abstract classes have at least one pure virtual function.

Example

class Animal {
public:
    // Virtual function — can be overridden
    virtual void speak() const {
        cout << "..." << endl;
    }
    virtual ~Animal() = default;
};

class Dog : public Animal {
public:
    void speak() const override {
        cout << "Woof!" << endl;
    }
};

class Cat : public Animal {
public:
    void speak() const override {
        cout << "Meow!" << endl;
    }
};

// Polymorphic behavior
void makeSound(const Animal& animal) {
    animal.speak();  // calls the correct version
}

Dog dog;
Cat cat;
makeSound(dog);  // "Woof!"
makeSound(cat);  // "Meow!"

// With pointers
vector<unique_ptr<Animal>> animals;
animals.push_back(make_unique<Dog>());
animals.push_back(make_unique<Cat>());
for (auto& a : animals) a->speak();