How can I call methods of inherited classes just by calling the same method of base class?

Question

Like in Game engines for example in XNA the update function is called automatically again and again. I want to know how i can achieve this in c++.

For ex:

class base
{
void Update();
};

class child1: public base
{
void Update();
}

class child2: public base
{
void Update();
}

void main()
{
base *obBase = new base();
obBase->Update(); /*This should call Update of Child1 and Child2 classes how can I do  this*/
}

Answer 1

Just make it virtual:

class base
{
    virtual void Update();
};

This will provide polymorphic behavior

And I assume you ment:

base *obBase = new child1(); //or new child2();

Answer 2

You can't access all instances of a derived classes of a base class.

What you need to do is to have some kind of a container, which will store all your objects of type Child1 and Child2 and then, when you decide, iterate through this container and call Update .

Something like:

SomeContainer< base* > myObjects;
// fill myObjects like:
// myObjects.insert( new ChildX(...) );
// ...
// iterate through myObjects and call Update

To be able to do this, you need to make Update a virtual function.

To prevent (potential) memory leaks, use smart pointers, instead of base* .

Answer 3

I guess you are trying to use polymorphism, something like this:

Base* obj1 = new Child1();
Base* obj2 = new Child2();

BaseManager* manager = new BaseManager(); //A class with a data struct that contains instances of Base, something like: list<Base*> m_objects;
manager->add(obj1); //Add obj1 to the list "m_objects"
manager->add(obj2); //Add obj2 to the list "m_objects"

manager->updateAll(); //Executes update of each instance in the list.