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From: bourd@buster.cps.msu.edu (Robert Bourdeau)
Newsgroups: comp.lang.c++
Subject: Re: asking an object for its type
Message-ID: <1991Feb14.144331.28031@msuinfo.cl.msu.edu>
Date: 14 Feb 91 14:43:31 GMT
References: <23984@netcom.COM>
Sender: news@msuinfo.cl.msu.edu
Reply-To: bourd@buster.cps.msu.edu (Robert Bourdeau)
Organization: Computer Science, Michigan State University, E. Lansing
Lines: 51

In article <23984@netcom.COM>, aed@netcom.COM (Andrew Davidson) writes:
|> Here is my problem, I have some processing that only applies for
|> certain types of objects. If an object is not of the correct type I
|> want to do some error stuff.
|> 
|> The problem is how do I fiqure out what the type of the object is. I
|> could return a string, ie provide an istype member function but then
|> the calling function would have to
|> know what the string is in advance, It also wont work with inheritance
|> 
|> Thanks Andy


Why not do what Borland did in their class library.

There is a header file use by the Borland class library called   clssname.h or
something like that, I can't remember exactly.

Anyway, it look something like

typedef    int			classType
#define    objectClass	 	0
#define	   containerClass	(objectClass+1)
#define	   collectionClass	(containerClass+1)

and so on....



The isA() member function for the class Container would loook something like:

class Container : Object {
	....

public:
	....
	classType isA() { return containerClass; }
	....
};



I am not sure how this is so terribly different from what you are proposing
above, except that it is more efficient.  Nevertheless, this idea will work
with inheritance (if I understand what you are stating your problem to be).


--- Robert Bourdeau
--- bourd@buster.cps.msu.edu
--- Michigan State University