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

[Branimir Maksimovic]

You are passing wchar_t* and function expects char*.


On 03/15/2014 12:23 AM, Miro Karpis wrote:
> here comes the c definition:
>
> int setmodulestring(char* parameter, int parameterLength, char* value, 
> int valueLength, int setVarInArray);
>
>
> In ghci the main and setmodulestring functions works fine
>
>
> On Sat, Mar 15, 2014 at 12:14 AM, Branimir Maksimovic 
> <branimir.maksimovic at gmail.com <mailto:branimir.maksimovic at gmail.com>> 
> wrote:
>
>     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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