[Haskell-cafe] ffi call works fine in ghci but not as ghc compiledsegfault

[Miro Karpis]

thank you very much - I have tried also that but got the the same behaviour
(seg fault)

cheers,
m.


On Sun, Mar 16, 2014 at 7:45 AM, Vagif Verdi <vagif.verdi at gmail.com> wrote:

> 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
>>
>>
>>
>>
>>
>>
>>
>>
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