[Haskell-beginners] How do I marshall a pointer over SendMessage LPARAM or WPARAM?

[Sylvain HENRY]

Are you sending the message to a window of the same process?

-Sylvain

Le 18/07/2012 18:28, Simon Peter Nicholls a écrit :
> I've tried that without joy. Have reposted over at Haskell cafe, as
> per Brent's advice. Thanks to both of you.
>
> On Wed, Jul 18, 2012 at 5:56 PM, Sylvain HENRY <hsyl20 at gmail.com> wrote:
>> Hi,
>>
>> [As I've just registered to the list, I don't have the original message.
>> That's why I answer to Brent insted of Simon]
>>
>> By using "withCWString", your CWString may be freed before the message is
>> sent. Use "newCWString" instead and "free" in your receiving code.
>>
>> Cheers
>> Sylvain
>>
>> Le 18/07/2012 17:47, Brent Yorgey a écrit :
>>
>>> Hi,
>>>
>>> Just a meta-comment: this doesn't seem like a beginner question to
>>> me. =) Perhaps someone on this list will know the answer (and there's
>>> nothing wrong with asking), but for such a specific question you may
>>> have better luck posting to haskell-cafe or StackOverflow.
>>>
>>> -Brent
>>>
>>> On Wed, Jul 18, 2012 at 03:14:46PM +0200, Simon Peter Nicholls wrote:
>>>> I'm new to Haskell, and have had some good success with FFI so far,
>>>> but using Win32's sendMessage to send a pointer in LPARAM or WPARAM is
>>>> resulting in access violations at the other end.
>>>>
>>>> Is there some issue with my pointer conversions? Am I hitting some
>>>> restriction, or missing some compiler options?
>>>>
>>>>
>>>>    It's driving me pretty crazy, after a very nice start to using Haskell.
>>>>
>>>> Some "sending" code:
>>>>
>>>>               Foreign.C.String.withCWString "frustrator" $ \s -> do
>>>>                   let wParam = System.Win32.Types.castPtrToUINT s ::
>>>> System.Win32.Types.WPARAM
>>>>                   Graphics.Win32.sendMessage wnd Graphics.Win32.wM_APP
>>>> wParam 0
>>>>
>>>> wndProc "receiving" code:
>>>>
>>>>       | wmsg == Graphics.Win32.wM_APP = do
>>>>           s <- peekCWString $ System.Win32.Types.castUINTToPtr wParam
>>>>           putStrLn s
>>>>           return 0
>>>>
>>>> The string will not be seen.
>>>>
>>>> Some extra notes:
>>>>
>>>> I can get wndProc messages and integral data generally.
>>>> The pointer values match textually at both ends when "shown" to stdout.
>>>> At the sending side I can pass the CWString to a regular FFI function
>>>> call just fine, and castUINTToPtr will give me back a functioning Ptr
>>>> for that call.
>>>>
>>>>    I have also tried sending to & receiving from a working C++ program,
>>>> without success. Access violations are reported when receiving, though
>>>> again the address matches up. Silence from Haskell as before, when C++
>>>> is sending.
>>>>
>>>> I found someone else having an issue here:
>>>> http://osdir.com/ml/haskell-cafe@haskell.org/2009-11/msg00731.html but
>>>> no solution unfortunately.
>>>>
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>>
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