RE: Passing a variable to a member class

=?Utf-8?B?QnJpYW4gTXV0aA==?= <>
Mon, 28 Jan 2008 21:00:27 -0800
This will work:

class A
  ToolClass myTool;
  B myB;

  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)



"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

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
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