From: Leah Neukirchen <leah@vuxu.org>
To: Bartosz Brachaczek <b.brachaczek@gmail.com>
Cc: musl@lists.openwall.com
Subject: Re: Documentation of memcpy and undefined behavior in memset
Date: Thu, 06 Jul 2017 21:10:31 +0200 [thread overview]
Message-ID: <8760f5s7o8.fsf@gmail.com> (raw)
In-Reply-To: <98d2e82c-1930-5dc2-2afa-bf6f4c9a8a50@gmail.com> (Bartosz Brachaczek's message of "Thu, 6 Jul 2017 21:05:12 +0200")
Bartosz Brachaczek <b.brachaczek@gmail.com> writes:
> On 7/6/2017 6:23 PM, Rich Felker wrote:
>> I think you're correct, at least under a pessimistic interpretation of
>> the standard. I can't find where they actually define "modifies", and
>> you could argue that assignment of the same value twice "modifies" the
>> object at most once, but I don't like relying on that kind of
>> ambiguity and it's easy enough to fix just by adding a sequence point.
>
> I don't have a copy of C11, but N1570 reads in a note to 3.1:
>
>> ‘‘Modify’’ includes the case where the new value being stored is the
>> same as the previous value.
C11 also specifies a sequence for assignment (6.5.16.3):
> The side effect of updating the stored value of the left operand is
> sequenced after the value computations of the left and right
> operands.
--
Leah Neukirchen <leah@vuxu.org> http://leah.zone
next prev parent reply other threads:[~2017-07-06 19:10 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-06 14:15 Pascal Cuoq
2017-07-06 15:52 ` Alexander Monakov
2017-07-06 16:23 ` Rich Felker
2017-07-06 17:02 ` Alexander Monakov
2017-07-06 17:11 ` Rich Felker
2017-07-06 17:17 ` Alexander Monakov
2017-07-06 17:22 ` Rich Felker
2017-07-06 17:38 ` Alexander Monakov
2017-07-06 18:13 ` Rich Felker
2017-07-06 18:52 ` Jens Gustedt
2017-07-06 19:23 ` Szabolcs Nagy
2017-07-06 23:52 ` Jens Gustedt
2017-07-06 19:05 ` Bartosz Brachaczek
2017-07-06 19:10 ` Leah Neukirchen [this message]
2017-07-06 19:28 ` Szabolcs Nagy
2017-07-06 16:29 ` Szabolcs Nagy
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