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Re: [wg14/wg21 liaison] Amendment to Next Week's Agenda

From: Aaron Ballman <aaron_at_[hidden]>
Date: Fri, 4 Feb 2022 15:09:25 -0500
On Thu, Feb 3, 2022 at 3:48 PM Jens Maurer via Liaison
<liaison_at_[hidden]> wrote:
> On 03/02/2022 13.36, Aaron Ballman via Liaison wrote:
> > I would like to add a paper to next week's agenda at the request of
> > WG14 (who are meeting this week for a plenary meeting).
> >
> > WG14 N2919 (http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2919.pdf)
> > Relax requirements for variadic parameter lists
> > This paper proposes allowing a function signature consisting solely of
> > an ellipsis in C (e.g., void foo(...);) and changes the va_start macro
> > so that its second argument is optional and never evaluated (only the
> > first parameter is used). The author is looking for feedback on
> > whether this proposal will cause compatibility concerns, as WG14 is
> > intending to add this feature to C23.
> The syntax "void foo(...)" is already supported in C++,
> so this part seems not an issue.

Personally agreed.

> It would be good to have an overview in the paper which (major)
> compilers already use some __builtin_va_start and which ones still
> look at parmN. If (the C modes of) all major C++ compilers already
> do the former without inspecting parmN, there doesn't seem to be an
> issue.
> (C++ would need to adjust [cstdarg.syn] for the modified
> va_start definition.)

Personally agreed.

The reason for the WG14 request is mostly due to the modified changes
to cstdarg.syn and whether there's any known issues with the direction
C is looking to go. I personally don't expect there to be surprises
here, but wanted to make sure SG22 was roped in just in case. JeanHeyd
has a draft paper in the works for the required changes to C++, which
will help ensure we don't forget to unify the two definitions.


> Jens
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Received on 2022-02-04 20:09:48