digitalmars.D.learn - C struct -> D struct (alignment hacks)
- Mike (28/28) Feb 04 2009 Hi!
- Jarrett Billingsley (12/37) Feb 04 2009 Nope. The C struct is defining a bitfield; a and b will actually be
Hi!
I'm in the process of translating some C headers (still ffmpef ->
libavcode and libavformat) to D and there are some really ugly structs in
the C headers which I'm trying to translate.
- C -
typedef struct xy
{
int a:1;
int b:2;
int c;
}
- D -
struct xy
{
align (1)
{
int a;
}
align (2)
{
int b;
}
int c;
}
Are those definitions equivalent?
-Mike
--
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Feb 04 2009
On Wed, Feb 4, 2009 at 2:55 PM, Mike <vertex gmx.at> wrote:
Hi!
I'm in the process of translating some C headers (still ffmpef -> libavcode
and libavformat) to D and there are some really ugly structs in the C
headers which I'm trying to translate.
- C -
typedef struct xy
{
int a:1;
int b:2;
int c;
}
- D -
struct xy
{
align (1)
{
int a;
}
align (2)
{
int b;
}
int c;
}
Are those definitions equivalent?
Nope. The C struct is defining a bitfield; a and b will actually be
contained within a single 4-byte field. Your D version defines three
integers.
Unfortunately the C specification does not specify any required
ordering for bitfields, padding, ordering etc. Fortunately, most
compilers just put them in order, starting from the lowest bits.
What you'll have to do, then, is put a single int field that
corresponds to the C struct's bitfields. Then, have methods which
shift and mask the bits to get and set the individual bitfields. htod
will do this for you, if you're on windows and just want to run an .h
file containing that struct through it.
Feb 04 2009
On Wed, 04 Feb 2009 21:04:16 +0100, Jarrett Billingsley <jarrett.billingsley gmail.com> wrote:Nope. The C struct is defining a bitfield; a and b will actually be contained within a single 4-byte field. Your D version defines three integers. Unfortunately the C specification does not specify any required ordering for bitfields, padding, ordering etc. Fortunately, most compilers just put them in order, starting from the lowest bits. What you'll have to do, then, is put a single int field that corresponds to the C struct's bitfields. Then, have methods which shift and mask the bits to get and set the individual bitfields. htod will do this for you, if you're on windows and just want to run an .h file containing that struct through it.Thanks. I tried htod with Wine, and although it runs it can't open include files, so I thought I'd translate the headers manually. However - I found more of those bitfields; I'll better find a machine with Windows then :) -- Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
Feb 04 2009
Don <nospam nospam.com> Mike wrote:On Wed, 04 Feb 2009 21:04:16 +0100, Jarrett Billingsley <jarrett.billingsley gmail.com> wrote:If you end up doing it manually, look in Phobos2, typecons.d has functions for generating bitfields. It'll work on D1 with trivial modifications.Nope. The C struct is defining a bitfield; a and b will actually be contained within a single 4-byte field. Your D version defines three integers. Unfortunately the C specification does not specify any required ordering for bitfields, padding, ordering etc. Fortunately, most compilers just put them in order, starting from the lowest bits. What you'll have to do, then, is put a single int field that corresponds to the C struct's bitfields. Then, have methods which shift and mask the bits to get and set the individual bitfields. htod will do this for you, if you're on windows and just want to run an .h file containing that struct through it.Thanks. I tried htod with Wine, and although it runs it can't open include files, so I thought I'd translate the headers manually. However - I found more of those bitfields; I'll better find a machine with Windows then :)
Feb 05 2009