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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