From: Paul Eggert <eggert@cs.ucla.edu>
To: Bruno Haible <bruno@clisp.org>,
bug-gnulib@gnu.org, Khem Raj <raj.khem@gmail.com>
Subject: Re: [PATCH] Define alignof_slot using _Alignof when using C11 or newer
Date: Sat, 14 Jan 2023 17:59:12 -0800 [thread overview]
Message-ID: <f3b2b750-bbf9-703b-b295-88bd379c4afc@cs.ucla.edu> (raw)
In-Reply-To: <4385269.dumfJixkPq@nimes>
On 2023-01-14 16:17, Bruno Haible wrote:
> What's (quasi) normative is
>
> * n3047.pdf = C23, which says in 7.21.(3)
> "If the specified type defines a new type or if the specified member is
> a bit-field, the behavior is undefined."
I'm afraid this wording in n3047 is unclear. Ordinarily one would look
at n3047's section "Type definitions" to interpret the phrase "defines a
new type", but as that section merely talks about typedefs it doesn't
seem to be relevant here. I can't find any part of the standard that
talks about "defining a new type".
All the standardizers wanted here is for the TYPE to not contain a
top-level comma in 'offsetof (TYPE, MEMBER)' because that would screw up
macro argument identification.
I hope Clang 16 is not reporting an error for 'offsetof (struct {char a;
int b;}, b)'; if so, it's gone off the deep end. A nameless struct does
not "define a new type" for some reasonable definitions of the term
"define a new type", and since the standard doesn't define that term the
Clang developers should be cautious about diagnostics in this messy area
when a lot of code out there uses offsetof in precisely this way.
prev parent reply other threads:[~2023-01-15 1:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-14 23:27 [PATCH] Define alignof_slot using _Alignof when using C11 or newer Khem Raj
2023-01-15 0:17 ` Bruno Haible
2023-01-15 1:20 ` Khem Raj
2023-01-15 1:59 ` Paul Eggert [this message]
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