C ++，找到父级并调用它的方法？

Question

I'd like to say that I have looked for a solution to this issue here but just could not find exactly what I was looking for. There may be a simple solution to my issue.

So take this example:

class Component
{
public:
    virtual ~Component() {} // Make Polymorphic;

    void Update() {};
};
class UserMadeComponent : public Component
{
public:

    void Update() {};
};

int main()
{
    std::vector<Component*> _components;

    UserMadeComponent* UsersComponent = new UserMadeComponent;

    _components.push_back(UsersComponent);

    while (true)
    {
        for (auto _comp = _components.begin(); _comp != _components.end(); _comp++)
        {
            (*_comp)->Update();
        }
    }
}

Now the programmer, using this framework, can create any type of component they want. And they will add this to the component vector. I want to be able to get the type of component and call its Update method. Here is a little diagram of what I am trying to accomplish:

So the goal is to call the "parents" update method. However, the user can create any type of component they'd like. I can't assume the type of any component inside this array. I hope this makes sense

//EDIT//

Thanks for people helping me to understand the virtual method calling. But how would I know what that class actually is. For example, the user has created a component called "Transform". I only want to allow one Transform instance in the component array. But obviously if I only know its a component pointer, I can't check for this occurrence.

It's hard to explain so here is another image:

Link to image

Answer 1

You're doing it backwards. Instead, create a virtual method called do_update that your derived classes override. The parent class's update method should call the virtual do_update method, which will dispatch properly.

This is how the Standard Library does it...

Answer 2

Use a virtual method.

Parent:

virtual void Update();

If you want the Component class to be "pure virtual," meaning you have to subclass it and it just represents an abstraction/interface, you can do:

virtual void Update() = 0;

This will give you an error if you try to instantiate a Component object, you create subclass objects only which implement all the pure virtual methods.

Edit:

The below code checks if x is a Transform. However, doing this means that you probably have a design flaw. Why not make a semantically aware container that stops a user from adding two transforms instead?

dynamic_cast<Transform*>(x) == nullptr