Date: Thu, 06 Jul 2017 21:10:31 +0200 From: Leah Neukirchen <leah@...u.org> To: Bartosz Brachaczek <b.brachaczek@...il.com> Cc: musl@...ts.openwall.com Subject: Re: Documentation of memcpy and undefined behavior in memset Bartosz Brachaczek <b.brachaczek@...il.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 (18.104.22.168): > 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@...u.org> http://leah.zone
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