Re: [Haskell-beginners] help with FFI: passing char* to dll function + pointer freeing

You should use the C variants of all the types, so type CBool = CInt foreign import stdcall unsafe "setmoduletable" c_setmoduletable :: CString -> CInt -> Ptr CDouble -> CInt -> CInt -> CBool -> IO CInt Edward Excerpts from Miro Karpis's message of Sat Sep 21 08:55:58 -0400 2013:

thanks,.. so far I came to this. I can compile it but not getting the right values from the method. Most probably some problem with the pointers...

---------------- --int setmoduletable(char *param, int length, double array[], int UB1, int UB2, bool isValid);

foreign import stdcall unsafe "setmoduletable" c_setmoduletable :: Ptr Char

-> Int

-> Ptr (Double)

-> Int

-> Int

-> Bool

-> IO Int

main = do let param = "Input_Bit_Nozz" let paramLength = length param realTable = [ 0.0111125, 0.0111125, 0.009525] :: [Double] ub1 = 0 ub2 = 2 isValid = False realTablePtr <- newArray realTable paramPtr <- newArray param x <- c_setmoduletable paramPtr paramLength realTablePtr ub1 ub2 isValid free realTablePtr free paramPtr putStrLn $ "c_setmoduletable output: " ++ show x putStrLn "Done"

On Sat, Sep 21, 2013 at 1:06 AM, Brandon Allbery wrote:

...

On Fri, Sep 20, 2013 at 6:53 PM, Miro Karpis wrote:

...

Please, I just can not figure this out:

I have a method in my C dll: int somemethod(char *param, int length, double array[], int UB1, int UB2, bool isValid);

I would like to use this method in Haskell, so I have defined it like:

foreign import stdcall unsafe "somemethod" c_somemethod :: Ptr CString

You don't want Ptr CString. See:

Prelude> :m +Foreign.C.String Prelude Foreign.C.String> :i CString type CString = GHC.Ptr.Ptr Foreign.C.Types.CChar -- Defined in `Foreign.C.String'

In other words, CString is an alias for Ptr CChar. Ptr CString corresponds to (char **), not (char *).

-- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net