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Date: Wed, 24 May 2023 10:22:01 -0400
From: Rich Felker <dalias@...c.org>
To: Jens Gustedt <Jens.Gustedt@...ia.fr>
Cc: musl@...ts.openwall.com
Subject: Re: [C23 divers headers 16/17] C23: add the nullptr_t type
On Wed, Apr 19, 2023 at 08:42:15AM +0200, Jens Gustedt wrote:
> This will only work with compilers that implement typeof and
> nullptr. Currently this doesn't work for gcc but this will probably be
> in gcc-13. Therefore the version test uses the future date of 202311L
> which is the foreseen value for C23 final.
>
> For clang there are better feature test macros, namely
> __is_identifier(nullptr) can be used to test if nullptr is an
> identifier or a keyword. In particular, this feature now seems to work
> with clang 16.0.2.
> ---
> include/stddef.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/include/stddef.h b/include/stddef.h
> index 09be5fb6..e4d6b2ef 100644
> --- a/include/stddef.h
> +++ b/include/stddef.h
> @@ -26,4 +26,14 @@
>
> #define unreachable() __builtin_unreachable()
>
> +#if __STDC_VERSION__ >= 202311L
> +typedef typeof(nullptr) nullptr_t;
> +#else
> +#if __clang__
> +#if !__is_identifier(nullptr)
> +typedef typeof(nullptr) nullptr_t;
> +#endif
> +#endif
> +#endif
> +
> #endif
> --
> 2.34.1
nullptr_t is not defined pre-C23 so the __clang__ branch shouldn't be
there.
Rich
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