allocate memory to Char **

[Lamine]

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 at gmail.com 
> <mailto: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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>


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