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From: mikem@otc.OZ (Mike Mowbray)
Newsgroups: comp.lang.c++
Subject: Re: Questions about C++
Message-ID: <134@otc.OZ>
Date: Thu, 2-Jul-87 06:22:59 EDT
Article-I.D.: otc.134
Posted: Thu Jul  2 06:22:59 1987
Date-Received: Sat, 4-Jul-87 06:11:24 EDT
References: <227@nih-csl.UUCP>
Distribution: comp
Organization: O.T.C. Systems Development, Australia
Lines: 27

In article <227@nih-csl.UUCP>, keith@nih-csl.UUCP (keith gorlen) says:
> Summary: Suggested technique for testing the class of an object
> 	 has some problems.
> 
> In article <131@otc.OZ>, mikem@otc.OZ (Mike Mowbray) writes:
>>
>> #define  IS_TYPE(classtype,instance)  ((instance)._vptr == ::classtype\
>> __vtbl)
>>		 [ ... deleted ... ]
>> //--------------------------------------------------------
> 
> This technique assumes that all instances of a class will have the
> same vtbl address, which is not true unless you use the +e compiler
> switch.
>		[ ... deleted ... ]
> Since using the +e switch is such a pain, I wouldn't recommend this method.

Agreed.

(Don't know why I mentioned this dubious method at all - I just thought
 it was an interesting curiosity.)

			Mike Mowbray
			Systems Development
			Overseas Telecommunications Commission (Australia)

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