C++ virtual Keyword

class Animal {
  public:
    virtual void animalSound() {
      cout << "The animal makes a sound\n";
    }
};

class Dog : public Animal {
  public:
    void animalSound() override {
      cout << "The dog says: bow wow\n";
    }
};

int main() {
  Dog myDog;
  Animal* a = &myDog;
  a->animalSound();
  return 0;
}

Definition and Usage

The virtual keyword specifies that a class method is virtual. A virtual method can be overridden (replaced) by a method with the same name in a child class.

When you call a virtual method through a pointer to the parent class, C++ checks the actual object, and runs its version of the method. In the example above, a points to a Dog, so the Dog version runs. Without virtual, the Animal version would run, and the output would be The animal makes a sound.

Use virtual only in the parent class. In the child class, you can write override after the method (optional, but recommended).

Related Pages

Read more about virtual functions in our C++ Virtual Functions Tutorial.

Read more about polymorphism in our C++ Polymorphism Tutorial.