On 03/14/2014 11:24 PM, Miroslav Karpis wrote:

Hi, please can you help me with following?

I have a call to an external dll (via ffi) which if executed from ghci works fine. 

If I compile my code with 'ghc -o fm Mycode.hs -L. -lextdll' and run it I get  'Segmentation fault/access violation in generated code'.

main = do

let param = "FilePath"

let value = "C:/dev/misc/haskell/services/FM"

result <- liftIO $ FM.setmodulestring param value

return "done"

setmodulestring :: String -> String -> IO CInt

setmodulestring param value = do

let cParamLength = fromIntegral $ length param ::CInt

    cValueLength = fromIntegral $ length value ::CInt

    setVarInArray = (-1)::CInt

alloca $ \cParam -> do

alloca $ \cValue -> do

result <- c_setmodulestring cParam cParamLength cValue cValueLength setVarInArray

return result

This does not seems correct (or incomplete).

If I try also with following, the behaviour is the same:

setmodulestring2 :: String -> String -> IO CInt

setmodulestring2 param value = do

cParam <- newCWString param

cValue <- newCWString value

let cParamLength = fromIntegral $ length param ::CInt

   cValueLength = fromIntegral $ length value ::CInt

   setVarInArray = (-1)::CInt 

result <- c_setmodulestring cParam cParamLength cValue cValueLength setVarInArray

free cParam

free cValue

return res

This one may be correct but without, seeing C code (where it probably
segfaults) I cannot say anything further.
exact ffi declaration of c_setmodulestring would be usefull, too,
to compare with C function.

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