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From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Olivier Hainque <hainque@adacore.com>,
	"libstdc++" <libstdc++@gcc.gnu.org>,
	gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Define _C99 in libstdc++ vxworks/os_defines.h
Date: Fri, 10 Dec 2021 15:42:46 +0000	[thread overview]
Message-ID: <CAH6eHdRjX+KmMsLbr-M75hyvj2PCxJ2RQ9iPaBmL1WpG_seowg@mail.gmail.com> (raw)
In-Reply-To: <3a28a096-3aec-7270-5e7b-9b8a54e4c7b9@prevas.dk>

On Fri, 10 Dec 2021 at 15:16, Rasmus Villemoes via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On 10/12/2021 16.06, Olivier Hainque wrote:
> > Hello,
> >
> > The attached patch for libstdc++ / VxWorks helps building
> > the library for old versions of the OS, as witnessed with
> > VxWorks 6.9 in particular.
> >
> > It explicitly requests C99 features from old system headers,
> > on which libstc++ relies since at least c++98. The specific
> > issue that exposed this was a failure to compile
> >
> >   libstdc++-v3/src/c++17/floating_to_chars.cc
> >
> > for VxWorks 6.9 with a batch of errors such as:
> >
> >   error: 'FP_NAN' was not declared in this scope
> >
> > The missing definitions are provided by the
> > system headers with guards on _HAS_C9X, which gets
> > internally defined when _C99 is.
> >
> > Ok to commit?
>
> Yes, we've observed that error as well. We have just patched our vxworks
> 5.5 headers to provide FP_NAN et al. There's no test of definedness or
> other uses of a _C99 macro anywhere, so ok by me, as it shouldn't change
> anything on our end.
>
> Rasmus

OK to commit then, thanks.

The comment is a bit misleading though:

+// libstdc++ relies on C99 features for virtually all versions of C++,
+// up to at least C++98.
+#undef _C99
+#define _C99 1

The "up to" seems backwards, I'd expect it to say "down to" or "as far
back as at least C++98".

But there's nothing older than C++98 anyway, so this just means "all
versions", there's no "virtually" about it.

Please just say "libstdc++ relies on C99 features for all versions of C++".

  reply	other threads:[~2021-12-10 15:42 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-10 15:06 Olivier Hainque
2021-12-10 15:15 ` Rasmus Villemoes
2021-12-10 15:42   ` Jonathan Wakely [this message]
2021-12-10 16:15     ` Olivier Hainque

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