Question

Can an inherited function call a function in the inheritor?

Asked by: Sowelu

Kind of hard to describe the question, and I don't have the source yet, so here goes...

Pretty much, let's say I have a window class, with six buttons on it. Three of these are standard close/minimise/resize buttons and it handles them itself... But there will be different 'types' of windows that will inherit this window class, and the three remaining buttons will do different things depending on what's inheriting it. So I want to have it pass a number to a function in the inheriting class.

So, if I have classes A, B1 and B2, and both B1 and B2 inherit from A...
Can a function in A, call a Foobar() function that's present in B1 and B2... but with entirely different code in each? My gut instinct tells me this is illegal because it's going by a pointer to the function, not by the name, but I'm not sure.

I hope I've made it clear enough... If it isn't, tell me what isn't clear and I'll try to clarify. I can't give source, because I need to know if I can do stuff this way... It'll be a lot of work I don't want to be wasted if it isn't possible.

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Asked On
2000-08-13 at 20:29:39ID10995582
Topic

C++ Programming Language

Participating Experts
2
Points
200
Comments
7

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Answers

 

by: avinash_sahayPosted on 2000-08-13 at 20:40:03ID: 3912513

I did not understand your question clearly.
A is your window class which handles the actions on the three standard buttons. For the remaining three buttons, if B1 inherits from A, then a function in A will call will call Foobar of B1. Similarly, if B2 inherits from A, then a function in A will call Foobar of B2.
But, it seems that both B1 and B2 inherit from A! When should Foobar of B1 and when should Foobar of B2 be called? Or, should both be called one after another?

 

by: SoweluPosted on 2000-08-13 at 20:47:24ID: 3912554

Well, at least the way I understand inheritance (and I'm new to C++) is that an object would just be B1 (and A), or B2 (and A).

What I'm trying to do with this, is have different windows for a game... Like, A would be all the code for a window in general, and B1 might be a toolbar, and B2 might be a map window.

I wouldn't need toolbar code on my map, or map code on my toolbar, so when A handles a mouse click on a button, and it isn't a button that's shared between all window types, it would let B1 or B2, whichever type the object is, take over and decide what to do with it...

 

by: avinash_sahayPosted on 2000-08-13 at 21:17:42ID: 3912711

>Well, at least the way I understand inheritance (and I'm new to C++) is that an object would just be B1 (and A), or B2 (and A).

It is wrong. You can always inherit more than one classes from a single parent.

 

by: avinash_sahayPosted on 2000-08-13 at 21:22:13ID: 3912736

Instead of inheriting B1 and B2 from A, you should make objects of type B1 and B2 as members of A. Then, you can call a function of any of these from a function in A, as appropriate.

 

by: gurpreetsPosted on 2000-08-13 at 21:24:00ID: 3912743

From my understanding of your question, I think the solution for you is polymorphism / RTTI. The three functions whose code is present in the derived classes, can be made virtual (in the base class). And I think you can implement like this -

class A
{
public:
virtual void func1()
{ ... }

.....

};

class B1 : public A
{
public:
void func1()
{ ... }

....
};

A*  a = new B1;
a->func1();

// This will execute the code written in B1.

Is your problem solved.









 

by: avinash_sahayPosted on 2000-08-13 at 21:30:53ID: 3912757

Hi gurpreets,
First of all, hearty congratulations to you for being expert of the week.

In Sowelu's problem, A knows that something has happened on a control and it want to delegate it to B1 or B2.

 

by: SoweluPosted on 2000-08-13 at 21:43:24ID: 3912786

It looks right and the source is a huge help -- Thanks! I'll have to give it a shot.

20120131-EE-VQP-002

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