Hi Sylvain,
thank you for your response! I try to use  this 2 lines

allocaArray (w*n) $ \var -> do
                  xs <- peekArray (w) var
to code

char **varnames = ccl_new_array (char *, w);

but it return [CString] not a [String]

On 04/29/2014 01:58 PM, Sylvain Henry wrote:

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@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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