[Haskell-beginners] help with FFI: passing char* to dll function + pointer freeing

[Brandon Allbery]

On Fri, Sep 20, 2013 at 6:53 PM, Miro Karpis <miroslav.karpis at gmail.com>wrote:

> Please, I just can not figure this out:
>
> I have a method in my C dll:
> int somemethod(char *param, int length, double array[], int UB1, int UB2,
> bool isValid);
>
> I would like to use this method in Haskell, so I have defined it like:
>
> foreign import stdcall unsafe "somemethod"  c_somemethod :: Ptr CString
>

You don't want Ptr CString.  See:

    Prelude> :m +Foreign.C.String
    Prelude Foreign.C.String> :i CString
    type CString = GHC.Ptr.Ptr Foreign.C.Types.CChar
  -- Defined in `Foreign.C.String'

In other words, CString is an alias for Ptr CChar. Ptr CString corresponds
to (char **), not (char *).

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/beginners/attachments/20130920/03ce491d/attachment.htm>