allocate memory to Char **

[Sylvain Henry]

Hi,

"varnames" is an array of pointers, you cannot allocate it with mallocBytes
(n*100).

Try something like this (not tested):

mallocList :: [String] -> IO (Ptr CString)
mallocList xs = newArray =<< forM xs g
  where
    g x = do
       b <- mallocBytes 100
       pokeCString b x 99
       return b

pokeCString :: CString -> String -> Int -> IO ()
pokeCString dst value maxLen = withCStringLen (take maxLen value) $ uncurry
(copyArray dst)

-Sylvain


2014-04-29 13:11 GMT+02:00 Lamine <mohamadoulamine at gmail.com>:

>
> Hi,
>
> I want to do write this C code in haskell code, but i have some pb:
>
> int w ;
> char **varnames = ccl_new_array (char *, w);
>
> int i;
>           for (i = 0; i < w; i++)
>             {
>               varnames[i] = ccl_new_array (char, 100);
>               sprintf (varnames[i], "x%d", i);
>             }
>
> I try this code unsing mallocList to (http://lpaste.net/report/712):
> mallocList :: [CString] -> IO (Ptr CString)
> mallocList xs = do let n = Prelude.length xs
>                    p <- mallocBytes (n*100)
>                    forM_ (Prelude.zip [0..] xs)
>                     (uncurry (pokeByteOff p))
>                    return p
>
> let n = sizeOf(undefined :: CString)
>            allocaArray w $ \var -> do
>                   xs <- peekArray (w*n) var
>                   varnames <- mallocList xs
>
> I have an error "segmentation fault(core dumped)".
> can someone please help me? Thank you.
>
> Lamine
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