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Date:	Mon, 29 Dec 2008 12:55:34 -0500
From:	Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Cygwin struct alignment
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On Mon, Dec 29, 2008 at 09:00:36AM -0000, John Emmas wrote:
>On Mon, Dec 24, 2008 at 19:47 Ralph Hempel wrote:
>>John, if I understand you correctly, you are running up against a
>>classic problem in embedded systems programming.  Namely that you
>>cannot assume anything about structure packing, byte ordering, or
>>alignment when doing RPC or transmitting data across platforms.
>
>Yesterday I spent some time looking into this but didn't come to any
>hard & fast conclusions.  Variables themselves seem to correlate very
>well between MSVC and Cygwin (even 'long' which I thought was
>different).  But when calculating structure alignment (manually)
>sometimes Cygwin gave closer results to what I expected and sometime
>MSVC was closer.
>
>Before I try Ralph's suggestion I'd like (if possible) to try building
>both versions with struct packing disabled.  This is fairly simple to
>do with Microsoft's compiler (I just set the member alignment to '1
>byte') but can it be done for my Cygwin compiler - e.g.  with a
>compiler option or a #pragma or whatever?

All of the pragmas should be discussed in the "info gcc" documentation.
Just go to the "Pragmas" node or search for "Pragmas Accepted by GCC".

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