C++: Create abstract class with abstract method and override the method in a subclass

Question

How to create in C++ an abstract class with some abstract methods that I want to override in a subclass? How should the .h file look? Is there a .cpp

Answer 1

The member functions need to be declared virtual in the base class. In Java, member functions are virtual by default; they are not in C++.

class GameObject
{
public:
    virtual void update() = 0;
    virtual void paint(Graphics g) = 0;
}

The virtual makes a member function virtual; the = 0 makes a member function pure virtual. This class is also abstract because it has at least one virtual member function that has no concrete final overrider.

Then in your derived class(es):

class Player : public GameObject
{
public:
    void update() { }          // overrides void GameObject::update()
    void paint(Graphics g) { } // overrides void GameObject::paint(Graphics)
}

If a member function is declared virtual in a base class, it is automatically virtual in any derived class (you can put virtual in the declaration in the derived class if you'd like, but it's optional).