Date: Sun, 02 Nov 1997 08:18:29 -0800 From: John Milford <jwm@CSUA.Berkeley.EDU> To: Christoph Kukulies <kuku@gilberto.physik.rwth-aachen.de> Cc: freebsd-hackers@freefall.freebsd.org Subject: Re: gcc and bitfields Message-ID: <199711021618.IAA02063@soda.CSUA.Berkeley.EDU> In-Reply-To: Message from Christoph Kukulies <kuku@gilberto.physik.RWTH-Aachen.DE> of "Sun, 02 Nov 1997 16:31:07 %2B0100." <199711021531.QAA04864@gil.physik.rwth-aachen.de>
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Christoph Kukulies <kuku@gilberto.physik.RWTH-Aachen.DE> wrote: > > 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? By default gcc pads structures to make make the size a multiple of 4 bytes. Try: struct C_OPEN { int a; int b; unsigned xdt:1; unsigned reserved:15; } __attribute__ ((packed)); --John
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