So... I'm still trying to write this Oracle OCI ffi binding. Can anyone tell me how to declare the Haskell type for this function: sword OCIEnvCreate (OCIEnv **envp, ub4 mode, dvoid *ctxp, dvoid *(*malocfp)(dvoid *ctxp, size_t size), dvoid *(*ralocfp)(dvoid *ctxp, dvoid *memptr, size_t newsize), void (*mfreefp)(dvoid *ctxp, dvoid *memptr), size_t xtramem_sz, dvoid **usrmempp); Note that when I use it, I'm passing 0 (NULL) into almost all of the args, so the usage in C is typically: rc = OCIEnvCreate(&envhp, OCI_DEFAULT, 0, 0, 0, 0, 0, 0); i.e. I don't care about most of the args, so that should make the Haskell declaration simpler. Some of the arguments are pointers to functions, for example. What I can't figure out is how to declare the type of the first arg. Is is Ptr (Ptr OCIEnv) ? Here's what I have so far (not much, I know):
module Main where import Foreign import Foreign.C.Types import Foreign.C.String import Foreign.Ptr
data OCIEnv
foreign import ccall "oci.h OCIEnvCreate" ociEnvCreate :: Ptr OCIEnv -> Int -> Int -> Int -> Int -> Int -> Int -> Int -> Int
-----Original Message-----
From: Ronald Legere [mailto:rjljr2@yahoo.com]
Sent: 21 May 2003 20:32
To: 'haskell-cafe@haskell.org'
Subject: Re: Help: writing ffi bindings to a C library
Agreeing with David, but I like to use
types rather than (). YOu can do this because,
in ghc, you can write:
data Blah
with no rhs, and it is understood to be an 'opaque'
type. Ghc beleives any claims you make about
passing Ptr Blah back and forth to C in your foreign
import declarations <* Grin *>.
As for passing structures back and forth, and
accessing the components, you can do it from Haskell
or from the "c-side"... I can send you a sample of
doing it from haskell if you wish.
Ron
--- David Roundy
On Wed, May 21, 2003 at 04:27:10PM +0100, Bayley, Alistair wrote:
construct a Ptr a? What type should "a" be?).
Unless you actually need to ever access their contents, I'd just define the pointers to be of type Ptr (), essentially like a void * pointer in C. No need to use Storable if they are only ever accessed through C functions (which I would hope would be the case). --
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