On Mon, Aug 20, 2007 at 05:27:04AM -0700, Ryan Ingram wrote:
I have a C function of type void f ( HsWord32* p0, HsWord32* p1, HsWord32 size );
along with the FFI declaration: foreign import ccall unsafe f :: Ptr Word32 -> Ptr Word32 -> Word32 -> IO ()
In my Haskell code I have an unboxed IO array of Word32; IOUArray Int Word32. I want to pass the pointer to this array to f(). How can I get the pointer out of the array? Or, is there a better way to declare f() to do this?
Short answer: You can't. Longer: GHC uses a copying/compacting garbage collector, so most objects don't have stable addresses. In particular MutableByteArray# is movable by default. So, you need an array structure built on pinned memory. If you want MArray operations, that leaves you with Data.Array.Storable, as already mentioned. Stefan