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<title>Issue 269: cstdarg and unnamed parameters</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#NAD">NAD</a> status.</em></p>
<h3 id="269"><a href="lwg-closed.html#269">269</a>. cstdarg and unnamed parameters</h3>
<p><b>Section:</b> 17.9 <a href="https://wg21.link/support.exception">[support.exception]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> J. Stephen Adamczyk <b>Opened:</b> 2000-10-10 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#support.exception">issues</a> in [support.exception].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>
One of our customers asks whether this is valid C++:
</p>

<pre>
   #include &lt;cstdarg&gt;

   void bar(const char *, va_list);

   void
   foo(const char *file, const char *, ...)
   {
     va_list ap;
     va_start(ap, file);
     bar(file, ap);
     va_end(ap);
   }
</pre>

<p>
The issue being whether it is valid to use cstdarg when the final
parameter before the &quot;...&quot; is unnamed.  cstdarg is, as far
as I can tell, inherited verbatim from the C standard. and the
definition there (7.8.1.1 in the ISO C89 standard) refers to &quot;the
identifier of the rightmost parameter&quot;.  What happens when there
is no such identifier?
</p>

<p>
My personal opinion is that this should be allowed, but some tweak
might be required in the C++ standard.
</p>


<p><b>Rationale:</b></p>
<p>
Not a defect, the C and C++ standards are clear.  It is impossible to
use varargs if the parameter immediately before &quot;...&quot; has no
name, because that is the parameter that must be passed to va_start.
The example given above is broken, because va_start is being passed
the wrong parameter.
</p>

<p>
There is no support for extending varargs to provide additional
functionality beyond what's currently there.  For reasons of C/C++
compatibility, it is especially important not to make gratuitous
changes in this part of the C++ standard.  The C committee has already
been requested not to touch this part of the C standard unless
necessary.
</p>




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