Re: Suggested FAQ entry

[Doug Semler <doug at seaspace dot com>]

> > Why?  This is an implementation issue, not a language issue...isn't it?
> 
> The fact that you MUST implement all virtual functions is a language
> requirement. [basic.def.odr] says
> 
> >> A virtual member function is used if it is not pure. ... Every
> >> program shall contain exactly one definition of every non­inline
> >> function or object that is used in that program; no diagnostic
> >> required.
> 
> The fact that violation of this requirement results in the diagnostic
> 'virtual table undefined' is an implementation issue.

Mea culpa.  And the diagnostic *is* emitted, in the linker, so it's
a little confusing...and, I admit, I read the docs for egcs and 
the faq, but skipped the standard :)

> 
> This *is* a FAQ, though, so having a FAQ entry might be a good
> idea. I'm not the FAQ maintainer, but if you provide a patch against
> http://egcs.cygnus.com/faq.html explaining the problem and the
> solution, I'm sure it will be accepted.
> 
> Regards,
> Martin

This is a patch against faq.html, I put it as the last entry in the
miscellaneous section, seemed to be only place it fits....and it may need
a little editing...I'm not that good with words :)

---
Doug Semler                       | doug@seaspace.com
SeaSpace Corporation              | Garbage In -- Gospel Out
Least Senior Software Developer;  | Minister of things to do Next Quarter
Low Man on the Totem Pole         | (but will Never Be Done) DNRC  O-
A closed mind is a terrible thing | Bus Error (passengers dumped)
  
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*** faq.html.orig	Sun Apr 11 17:20:22 1999
--- faq.html	Sun Apr 11 17:29:14 1999
***************
*** 98,103 ****
--- 98,104 ----
  	 (<tt>-fsquangle</tt>)</a>
      <li><a href="#gperf">When building from CVS sources, I see 'gperf: invalid option -- F', 
  	even with the most current version of gperf.</a>
+     <li><a href="#vtables">When building C++, the linker says my constructors, destructors or virtual tables are undefined, but I defined them</a>
    </ol>
  </ol>
  
***************
*** 1166,1171 ****
--- 1167,1182 ----
  
  <hr>
  
+ <h2><a name="vtables">When building C++, the linker says my constructors, destructors or virtual tables are undefined, but I defined them</a></h2>
+ 
+ <p>The C++ language specifies that all virtual methods that are declared must
+ be defined.  The linker error message is telling you that at least one
+ of the virtual methods declared has not been defined, as the constructors,
+ destructor, and virtual table was never emitted by egcs for the class. 
+ 
+ <p>The solution is to ensure all virtual methods are defined.
+ 
+ <hr>
  
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  <p><i>Last modified:  March 29, 1999</i>