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From: mneerach@c.inf.ethz.ch (Matthias Ulrich Neeracher)
Newsgroups: comp.lang.c++
Subject: Re: Re vectors and clobbering.  Hashing defect?
Message-ID: <53@neptune.inf.ethz.ch>
Date: 16 Jul 90 13:07:39 GMT
References: <6570@helios.TAMU.EDU>
Sender: news@neptune.inf.ethz.ch
Reply-To: mneerach@c.inf.ethz.ch (Matthias Ulrich Neeracher)
Lines: 31

In article <6570@helios.TAMU.EDU> jeffw@cs.tamu.edu (Jeffrey A Waller) writes:
>MY QUESTION IS:
>
>What is __ptbl used for anyway, and is it possible that a hashing collision
>has occured to give the multiply defined symbols error.

I think __ptbl's are used for multiple inheritance and virtual members. 
Every object belonging to a class with virtual members contains pointers
to a __vtbl and a __ptbl specific to this class. Now, if somebody calls
virtual member #i of this class, __ptbl[i] is added to 'this' and the 
member function pointed to by __vtbl[i] is called (Actually, it might
also be the otherway around).
   Now, your multiply defined symbol error: I got this from the Apple MPW
C++ manuals. C++ has to decide in which file to put the __vtbl and __ptbl
of a class, which are static tables, if the class members are scattered 
across multiple files. Normally these tables are put into the file which
contains the definition of the first non-virtual non-inline member or so.
If no such member exists, the tables are put into every file that contains
member definitions for this class. I don't know of any workaround.
  On the other hand, you can safely ignore these warnings, as all the
conflicting symbols contain identical data.

>						-Jeff Waller
>        					jeffw@cssun.tamu.edu

Matthias

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* Matthias Neeracher   * I wouldn't recommend sex, drugs or insanity for  *
* mneerach@inf.ethz.ch * everyone, but they've always worked for me - HST *
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