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Date: Fri, 5 May 2023 08:56:41 +0200
From: Jₑₙₛ Gustedt <jens.gustedt@...ia.fr>
To: JeanHeyd Meneide <phdofthehouse@...il.com>
Cc: musl@...ts.openwall.com, enh <enh@...gle.com>, Rich Felker
<dalias@...c.org>, "罗勇刚(Yonggang Luo)"
<luoyonggang@...il.com>, Jason Ekstrand <jason@...kstrand.net>
Subject: Re: C23 implications for C libraries
Hello,
on Thu, 4 May 2023 20:37:58 -0400 you (JeanHeyd Meneide
<phdofthehouse@...il.com>) wrote:
> > for example, stuff like the %B specifier are technically optional
> > given
> that the uppercase conversion specifier namespace wasn't reserved,
> but iirc there's no known implementation of C that uses it for any >
> other purpose.
>
> There was apparently one implementation that was already using
> %B as a kind of numeric printout (not for binary) that was reported
> during the meeting and at a few other junctures, so unfortunately it
> might not be fully portable. …
Yes, in general I am always amazed to see how diversive and inventive
C implementations are. So changing things even as innocent sounding
like a format specifier or adding new function identifiers that could
be conflicting with applications is usually watched very
closely. There are really a lot of C implementations out there, and
in general they use the design space that is offered to them.
For format specifiers this is even more complicated. There are C
libraries that provide interfaces to add such specifiers from user
space. So here the risk for conflicts can not easily be assessed by
WG14 (we don't have the data). So it should be left to the C library
implementors to assess this risk.
Thanks
Jₑₙₛ
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