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

14 Mar 2014


      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 
mailto:branimir.maksimovic@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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