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

If you are doing inter-process communication, you should not send pointers as processes do not share the same address space. Use WM_COPYDATA to send a specific amount of data. http://msdn.microsoft.com/en-us/library/windows/desktop/ms649011%28v=vs.85%2... I've read that SendMessage is blocking, so you can use withCWString (contrary to what I have previously written). As you have to pass the size of the data, you can even use withCWStringLen (and peekCWStringLen). Cheers Sylvain Le 18/07/2012 19:02, Simon Peter Nicholls a écrit :

It's inter-process by design.

I have a small "single instance " C++ program that I'm porting to Haskell. Once the first instance launched is up and running, subsequent launches send their command line params through to the single instance (file names). Similar to when a media player queues files in a play list.

The most recent extra clue I have is that if I wrap the SendMessage function with my own C FFI version, my C function can both re-cast and output the CWString I have sent, and can successfully invoke the real SendMessage by overriding the CWString with a newly created L"blah" string. It's just a shame it can't use the original!

My next session will involve poking around at the two strings to learn why they are treated differently.

On Wed, Jul 18, 2012 at 6:33 PM, Sylvain HENRY wrote:

...

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 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.

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

---

Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

---

Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

---

Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners