Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| Path | csiph.com!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail |
|---|---|
| From | Tim Rentsch <tr.17687@z991.linuxsc.com> |
| Newsgroups | comp.std.c |
| Subject | Re: Why doesn't __VA_LIST__ just eat the prior comma? |
| Date | Tue, 19 Apr 2022 02:04:36 -0700 |
| Organization | A noiseless patient Spider |
| Lines | 22 |
| Message-ID | <861qxta1gb.fsf@linuxsc.com> (permalink) |
| References | <20220413165157.844@kylheku.com> |
| Mime-Version | 1.0 |
| Content-Type | text/plain; charset=us-ascii |
| Injection-Info | reader02.eternal-september.org; posting-host="dca78489ef0b00bc0e84cad62da1ae52"; logging-data="20574"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18LHuRw5OrqTjaWqrVio5BrLCtWd1Ro6i0=" |
| User-Agent | Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux) |
| Cancel-Lock | sha1:coSXZqNNssDjeDkUa1AqGGOG4Jg= sha1:rZG0t51L3MfwOmd/QFAEfrh/a04= |
| Xref | csiph.com comp.std.c:6434 |
Show key headers only | View raw
Kaz Kylheku <480-992-1380@kylheku.com> writes:
> There is a well-known problem that a macro like
>
> #define foo(x, ...) something(whatever, __VA_ARGS__)
>
> cannot work when the trailing argument list is empty because
> you get the expansion something(whatever, )
>
> GNU C provides ##__VA_ARGS__ which behaves like __VA_ARGS__ in
> the nonempty case, and eats the prior comma in the empty case.
>
> C++20 provides __VA_OPT__ which is used like __VA_OPT__(,) to
> conditionally eat the comma. (GNU C has this also).
>
> The question is: why wouldn't you just fix the semantics of
> __VA_ARG__ so that this is not necessary?
This idea is considered in section "Alternative Designs" of
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2160.htm
Back to comp.std.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Why doesn't __VA_LIST__ just eat the prior comma? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-04-14 00:01 +0000
Re: Why doesn't __VA_LIST__ just eat the prior comma? Ben <ben.usenet@bsb.me.uk> - 2022-04-14 14:17 +0100
Re: Why doesn't __VA_LIST__ just eat the prior comma? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-04-18 16:59 +0000
Re: Why doesn't __VA_LIST__ just eat the prior comma? Ben <ben.usenet@bsb.me.uk> - 2022-04-18 20:43 +0100
Re: Why doesn't __VA_LIST__ just eat the prior comma? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-04-19 02:04 -0700
Re: Why doesn't __VA_LIST__ just eat the prior comma? Kaz Kylheku <480-992-1380@kylheku.com> - 2022-04-20 02:02 +0000
Re: Why doesn't __VA_LIST__ just eat the prior comma? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-05-14 10:35 -0700
csiph-web