ryani.spam:

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?

I'm open to using GHC hackery; using v6.6.1 right now.

Perhaps you want to use Foreign.Array instead (they are unboxed, and can be used as a Ptr over to C land)? -- Don

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