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From: rcb@ccpv1.ncsu.edu (Randy Buckland)
Newsgroups: comp.lang.c++
Subject: Determining an object's class
Message-ID: <1990Feb13.202006.29601@ncsuvx.ncsu.edu>
Date: 13 Feb 90 20:20:06 GMT
Sender: news@ncsuvx.ncsu.edu (USENET News System)
Distribution: comp
Organization: NCSU Computing Center
Lines: 38

Is it possible in C++ to determine if an object is a member of a certain
subclass? For example:

----------------------------------------------------------------------------
class foo { ... };
class bar : public foo { ... };

foo *aFunction ();

code()
{
	foo *a_foo;
	bar *a_bar;

	a_foo = aFunction();

	/*********** Here's what I want to do **************/
	if (is_class (a_foo, foo)) {
	...
	}
}
----------------------------------------------------------------------------

What I want to be able to do is to have an object that can contain a set of
objects of type "foo" or one of it's subclasses. I will have operations that 
can be done to all members of the set and all classes based on "foo" will
support. This I can do. However, I want to be able to extract an object
from the set and if it is really a member of the subclass, call an extra
method that only the subclass supports. 

I could brute force it with a variable/function that hold's the object
type, but this seems wasteful.

(Oh for a real, compiled, OO language on ultrix. Eiffel does not qualify
since it break's every time I use it.)

Randy Buckland
rcb@ncsuvx.ncsu.edu