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To: Christoph Kukulies <kuku@gilberto.physik.RWTH-Aachen.DE>
cc: freebsd-hackers@freefall.FreeBSD.org
Subject: Re: gcc and bitfields 
In-reply-to: Your message of "Sun, 02 Nov 1997 16:31:07 BST."
             <199711021531.QAA04864@gil.physik.rwth-aachen.de> 
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Date: Mon, 03 Nov 1997 11:21:15 +1030
From: Mike Smith <mike@smith.net.au>
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> 
> During porting a piece of a DOS program to make a driver
> for FreeBSD of it for a certain device I'm stuck at the
> point where there is a structure:
> 
>     struct C_OPEN {
>          int a;
>          int b;
>          unsigned xdt:1;
>          unsigned reserved:15;
>     }
> 
> The sizeof this structure is 10 under DOS (borland C)
> and evaluates to 12 under cc (gcc) on FreeBSD.
> 
> There are a lot of these definitions and it would be
> tedious to find a workaround.
> 
> Does anyone know if I can pack the structure respectively
> enforce the bitfield to a short int?

 __attribute__ ((packed))

(Read the info entry on gcc, under 'C extensions/Variable Attributes'.

mike