Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!cs.utexas.edu!helios!cs.tamu.edu!jeffw
From: jeffw@cs.tamu.edu (Jeffrey A Waller)
Newsgroups: comp.lang.c++
Subject: Re: c++ 2.0 upgrade from 1.2.?
Message-ID: <4663@helios.TAMU.EDU>
Date: 25 Mar 90 05:23:00 GMT
Sender: usenet@helios.TAMU.EDU
Reply-To: jeffw@cs.tamu.edu (Jeffrey A Waller)
Distribution: usa
Organization: Computer Science Department, Texas A&M University
Lines: 111

<tuck@jason.cs.unc.edu> writes:

>article <12801@thorin.cs.unc.edu> frederic@vangogh.cs.unc.edu (Robin Frederick
sen) writes:
>>I am upgrading some software from C++1.2.? to C++2.0.  It seems that
>>there is something missing.  At link time I get the message
>>
>>       Undefined:
>>       __ptbl__9ih_editor__ih_editor_c
>>       *** Error code 1

>Does your C++ program call a routine named "ih_editor" that was compiled
>with plain C?  If so, you need to put the declaration of "ih_editor" that
>C++ sees inside the {}s of

>  extern "C" {    }

>Just a guess.  One of the main changes from 1.2 to 2.0 is type-safe
>linking, which means encoding argument types in the mangled names of
>functions to be sure the calls and the definition match (even when
>compiled separately) and to support overloading better.  To call
>something C compiled, you have to tell C++ that C didn't mangle the
>name.

No, I don't think that that is the problem.  If it is let me know.  However,
I have had (and still do) the same problem.  Here are the error messages
generated by the linker:

___ptbl__18connected__gsocket_l3: ld: inetserver.o: multiply defined
___ptbl__19fdmessager__gsocketUe: inetserver.o: multiply defined
___ptbl__18connected__gsocket_l3: inetsocket.o: multiply defined
___ptbl__19fdmessager__gsocketUe: inetsocket.o: multiply defined
___ptbl__18connected__gsocket_l3: unixclient.o: multiply defined
___ptbl__19fdmessager__gsocketUe: unixclient.o: multiply defined
___ptbl__18connected__gsocket_l3: unixserver.o: multiply defined
___ptbl__8messager__12serversoxA: unixserver.o: multiply defined
___ptbl__19fdmessager__gsocketUe: unixserver.o: multiply defined
___ptbl__18connected__gsocket_l3: unixsocket.o: multiply defined
___ptbl__19fdmessager__gsocketUe: unixsocket.o: multiply defined

Concerning the symbol ___ptbl__19fdmessager__gsocketUe in inetserver.o, I
looked at the c code generated by CC (2.0 that is), and after running the
output through c++filt the above symbol equates to the following:


Around line 164 in transformed inetserver..c

extern struct __mptr* fdmessager__gsocket::_ptbl


Looking on in the file, sure enough the thing is defined again:


Around line 324 in transformed inetserver..c

struct __mptr* fdmessager__gsocket::_ptbl      = fdmessager__gsocket::_vtbl;


I've never heard of ___ptbl anything although aparently it has something to
due with the virtual function table, and with later experiments
(described later) I think that it has something to do with multiple
inheritance and virtual base classes.

So, I try some stuff including +w +e1 +e0 compiler options, but the
error messages remain unaffected. At this point let me digress
(still further) and give the original class inheritance scheme.


class messager                             // classes that pass messages around

class fdmessager: public virtual messager  // ditto, except by file descriptors

class taggedio: public virtual messager    // a certian protocol of messageing

class connected            // classes referring to same thing form linked list 

class gsocket:public fdmessager,public taggedio,public connected

class inetsocket:public virtual gsocket

class unixsocket:public virtual gsocket

class clientsocket:public virtual gsocket

class serversocket:public virtual gsocket

class inetserver:public inetsocket,public serversocket

class unixserver:public unixsocket,public serversocket

class inetclient:public inetsocket,public clientsocket

class unixserver:public unixsocket,public clientsocket

So for some reson--grasping at straws-- I change the definition of gsocket
a little, and THAT IS ALL THAT WAS CHANGED, to the following

class gsocket:public virtual fdmessager,public virtual taggedio,public connected

Suddenly the new linker error messages are the following:

___ptbl__10fdmessager__10inetsUt: ld: inetsocket.o: multiply defined
___ptbl__8messager__12serversoxA: unixserver.o: multiply defined
___ptbl__8taggedio__12serversoxA: unixserver.o: multiply defined
___ptbl__10fdmessager__10unixsxd: unixsocket.o: multiply defined

This is my first forray into multiple inheritance so I havn't the foggiest
how to fix things.  I someone has similar problems, or at least more
experience please let me know.

e-mail: jeffw@cssun.tamu.edu