Message-ID: <004701c96993$ea2fa5f0$4001a8c0@mycomputer>
From: "John Emmas" <johne53@tiscali.co.uk>
To: <cygwin@cygwin.com>
References: <006b01c965c1$6a7c6300$4001a8c0@mycomputer> <003a01c965fe$539063c0$4001a8c0@mycomputer> <495291CD.1000207@bmts.com>
Subject: Re: Cygwin struct alignment
Date: Mon, 29 Dec 2008 09:00:36 -0000
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----- Original Message ----- 
From: "Ralph Hempel"
Sent: 24 December 2008 19:47
Subject: Re: Cygwin struct alignment
>
> 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?

Thanks,

John 


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