I do not think i can help you, but my FFi to functions with similar signature looks like this:
C definition:
PDFLIB_API int PDFLIB_CALL
PDF_begin_document(PDF *p, const char *filename, int len, const char *optlist);
haskell FFI:
c_beginDocument :: Pdf -> String -> String -> IO Int
c_beginDocument pdf a2 a3 =
withCString a2 $ \a2' ->
withCString a3 $ c_beginDocument'_ pdf a2' 0
foreign import ccall safe "Pdflib.chs.h PDF_begin_document" c_beginDocument'_ :: Pdf -> Ptr CChar -> CInt -> Ptr CChar -> IO Int
The difference as you see, i'm using withCString to convert from ahskell to C and i'm passing 0 as the string size.
On Friday, March 14, 2014 3:24:23 PM UTC-7, 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
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
Any comments/ideas more than appreciated.
Cheers,
Miro