Re: [PATCH] builtin/mv.c: use correct type to compute size of an array element

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 7, 2022, 20:25 UTC
Message-ID: <xmqqfsjczn42.fsf@gitster.g>
In-Reply-To: <YscpDTgwxUko/aZM@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

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> On Wed, Jul 06, 2022 at 07:02:18PM -0700, Junio C Hamano wrote:
>
>>    * Should we in general use sizeof(TYPE) in these cases, instead
>>      of the size of the zeroth element, e.g.
>> 
>>  		memmove(source + i, source + i + 1,
>> 			n * sizeof(source[i]));
>>     
>>      It would have been caught by the above Coccinelle rule (we are
>>      taking the size of *dst).
>
> I'm not sure I understand this. As you noted in a later email, using
> sizeof(TYPE) is less maintainable if the type of "source" changes.

Sorry for a typo or thinko, whichever one you like ;-)

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> But
> later you mention using "*source" instead of "source[i]". I don't think
> there is a particular reason to prefer one over the other from the
> compiler perspective. I find "*source" more idiomatic (but better still
> of course is MOVE_ARRAY, which removes the choice entirely).

Yes, I wrote source[i] there only because I found it somewhat awkward to write source[0] or *source there, when the moved (sub)array is from the index 'i' to the end. *(source + i) would have matched the intention better but it still is awkward.