RE: Passing a variable to a member class

From:

=?Utf-8?B?QnJpYW4gTXV0aA==?= <BrianMuth@discussions.microsoft.com>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 28 Jan 2008 21:00:27 -0800

Message-ID:

<5D7DDD41-1684-455C-A45A-F1195420D1DE@microsoft.com>

This will work:

class A
{
  ToolClass myTool;
  B myB;

public:
  class A ()
  : myTool (),
    myB (&myTool)
  {
  }
};

However, I'd like to add that this is very poor design as it defeats some of
the principles of OOP. Perhaps it makes more sense to derive B from
ToolClass? (ie. use inheritance)

HTH

Brian

"Zapanaz" wrote:

This seems like a stupid question ... it's fairly basic but I am not
seeing it.

I have a class, class A, which has a member, a second class, call it
ToolClass.

Class A also has a member which is an instance of class B.

So I have

class A
{
  ToolClass myTool;
  B myB;
}

Now I have class B, which needs to have a pointer to the same instance
of ToolClass as class A, it's important that they be the same
instance. Class B needs this when it is instantiating.

class B
{
  ToolClass * myTool;
}

So class A instantiates, the constructor for ToolClass is called to
create A.myTool, then the default constructor for class B is called.
(I could set the pointer into myB.myTool in the constructor of A, but
the constructor of B is already called before execution actually
enters the constructor of A).

I can add a constructor to B that allows me to pass in &myTool ... it
seems like that ought to be simple, but I am not seeing how to do it.

I declare the member object in class A, myB, which is of class B.
This causes the default constructor of class B to be called, which
doesn't have a pointer to myTool, which it needs during it's
constructor execution.

I could make the default constructor something like B(ToolClass *
myTool=NULL), but that doesn't really help.

So am I missing something obvious? It seems like there has to be a
way to do this ... or maybe not, maybe that's forbidden because I
can't necessarily depend on the ToolClass object being constructed
before myB.

--
Joe Cosby
http://joecosby.com/
HellPope Pinata:
     beat me with a stick, I'm full of candy

:: Currently listening to St. Jimmy, 2004, by Green Day, from "American Idiot"