From: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Date: Tue, 26 Aug 2014 12:59:52 GMT
Subject: Re: [PATCH] bisect: save heap memory. allocate only the required amount
Message-ID: <53FC84C8.1020300@ramsay1.demon.co.uk>
In-Reply-To: <20140826124344.GF29180@peff.net>

On 26/08/14 13:43, Jeff King wrote:
> On Tue, Aug 26, 2014 at 01:37:44PM +0100, Ramsay Jones wrote:
> 
>>> On my 64-bit system using gcc, sizeof() returns 16; it has to pad the
>>> whole thing to 64-bit alignment in case I put two of them in an array.
>>> But offsetof(name) is 12, since the array of char does not need the same
>>> alignment; it can go right after the type and make use of the padding
>>> bits.
>>
>> Hmm, interesting. I must re-read the standard. I was convinced that the
>> standard *requires* any alignment padding to come *before* the name field.
>> (how would you put a, non-trivial, variable data structure into an array?)
> 
> I think you don't. How would you compute a[1] if a[0] has a variable
> size?
> 
> You can put a flex-array structure into an array, but then each element
> has the flex member as zero-size (and you should not access it, of
> course).

Exactly. ;-)

ATB,
Ramsay Jones