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    CWG Issue 506</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="506"></A><H4>506.
  
Conditionally-supported behavior for non-POD objects passed to ellipsis
</H4>
<B>Section: </B>7.6.1.3&#160; [<A href="https://wg21.link/expr.call">expr.call</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD1
 &#160;&#160;&#160;

 <B>Submitter: </B>Mike Miller
 &#160;&#160;&#160;

 <B>Date: </B>14 Apr 2005<BR>


<P>[Voted into WP at the October, 2006 meeting.]</P>

<P>The current wording of 7.6.1.3 [<A href="https://wg21.link/expr.call#7">expr.call</A>] paragraph 7
states:</P>

<BLOCKQUOTE>

When there is no parameter for a given argument, the argument is
passed in such a way that the receiving function can obtain the
value of the argument by invoking <TT>va_arg</TT>
(17.14 [<A href="https://wg21.link/support.runtime">support.runtime</A>]).  The lvalue-to-rvalue
(7.3.2 [<A href="https://wg21.link/conv.lval">conv.lval</A>]), array-to-pointer
(7.3.3 [<A href="https://wg21.link/conv.array">conv.array</A>]), and function-to-pointer
(7.3.4 [<A href="https://wg21.link/conv.func">conv.func</A>]) standard conversions are performed
on the argument expression.  After these conversions, if the
argument does not have arithmetic, enumeration, pointer,
pointer to member, or class type, the program is ill-formed.
If the argument has a non-POD class type (
Clause 11 [<A href="https://wg21.link/class">class</A>]), the behavior is undefined.

</BLOCKQUOTE>

<P>Paper J16/04-0167=WG21 N1727 suggests that passing a non-POD
object to ellipsis be ill-formed.  In discussions at the
Lillehammer meeting, however, the CWG felt that the newly-approved
category of conditionally-supported behavior would be more
appropriate.</P>

<P><B>Proposed resolution (October, 2005):</B></P>

<P>Change 7.6.1.3 [<A href="https://wg21.link/expr.call#7">expr.call</A>] paragraph 7 as indicated:</P>

<BLOCKQUOTE>

...After these conversions, if the argument does not have arithmetic,
enumeration, pointer, pointer to member, or class type, the program is
ill-formed. <DEL>If the argument has a non-POD class type (clause 9),
the behavior is undefined.</DEL> <INS>Passing an argument of non-POD class
type (clause 9) with no corresponding parameter is
conditionally-supported, with implementation-defined semantics.</INS>

</BLOCKQUOTE>

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