allocate memory to Char **

[Sylvain Henry]

To create the [String] as in your example, you just have to write:

let names = ["x"++ show i | i <- [0..w-1]]
varnames <- mallocList names

-Sylvain


2014-04-29 15:40 GMT+02:00 Lamine <mohamadoulamine at gmail.com>:

>  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>:
>
>>
>> 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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>>
>
>
>
> --
> « Chaque génération doit, dans un état relatif de captivité, découvrir sa
> mission. Elle a le choix de la remplir ou la trahir». Frantz Fanon
>
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