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    CWG Issue 722</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="722"></A><H4>722.
  
Can <TT>nullptr</TT> be passed to an 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>CD2
 &#160;&#160;&#160;

 <B>Submitter: </B>Alisdair Meredith
 &#160;&#160;&#160;

 <B>Date: </B>25 September, 2008<BR>


<P>[Voted into WP at March, 2010 meeting.]</P>

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

<BLOCKQUOTE>

After these conversions, if the argument does not have
arithmetic, enumeration, pointer, pointer to member, or effective
class type, the program is ill-formed.

</BLOCKQUOTE>

<P>It's not clear whether this is intended to exclude anything other
than <TT>void</TT>, but the effect is to disallow passing
<TT>nullptr</TT> to ellipsis.  That seems unnecessary.</P>

<P><B>Notes from the October, 2009 meeting:</B></P>

<P>The CWG agreed that this should be supported and the effect
should be like passing <TT>(void*)nullptr</TT>.</P>

<P><B>Proposed resolution (February, 2010):</B></P>

<P>Change 7.6.1.3 [<A href="https://wg21.link/expr.call#7">expr.call</A>] paragraph 7 as follows:</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>]). [<I>Note:</I> This paragraph does not apply to
arguments passed to a function parameter pack.  Function
parameter packs are expanded during template instantiation
(13.7.4 [<A href="https://wg21.link/temp.variadic">temp.variadic</A>]), thus each such argument has a
corresponding parameter when a function template specialization
is actually called. &#8212;<I>end note</I>] 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.
<INS>An argument that has (possibly cv-qualified) type
<TT>std::nullptr_t</TT> is converted to type <TT>void*</TT>
(7.3.12 [<A href="https://wg21.link/conv.ptr">conv.ptr</A>]).</INS> After these conversions...

</BLOCKQUOTE>

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