Which message numbers belong to whom?

RE: Which message numbers belong to whom?

KiwiBlue — Tue, 02 Dec 2003 19:36:00 GMT

I remember reading somewhere that for backward compatibility reasons Windows will actually marshall cross-process messages above WM_USER for classes like listbox etc. Can you comment on that?

RE: Which message numbers belong to whom?

Raymond Chen — Tue, 02 Dec 2003 20:13:00 GMT

If you look closely at winuser.h, you'll see that all those messages got renumbered to be below WM_USER. #define LB_ADDSTRING 0x0180 #define LB_INSERTSTRING 0x0181 etc.

RE: Which message numbers belong to whom?

KiwiBlue — Tue, 02 Dec 2003 21:04:00 GMT

You're right. The funny thing is that LB_ADDSTRING is also #defined in winres.h as (WM_USER + 1), at least in SDK which ships with VC6.

RE: Which message numbers belong to whom?

Jordan Russell — Wed, 03 Dec 2003 01:21:00 GMT

There isn't any way to free a registered message, is there?

RE: Which message numbers belong to whom?

Jordan Russell — Wed, 03 Dec 2003 01:38:00 GMT

Oh, something else I've always wondered: What is *supposed* to happen when the registered message pool is exhausted? It seems that (on Windows 2000) RegisterWindowMessage() will loop back to 0xC000 and start returning identifiers that were already registered under different names. Is this intentional?

RE: Which message numbers belong to whom?

John Schroedl — Wed, 03 Dec 2003 04:24:00 GMT

Speaking of Atoms..how about a posting about their uses/merits/etc. I rarely think to use one..when should I? Thanks for a great blog!

RE: Which message numbers belong to whom?

Anonymous — Wed, 03 Dec 2003 08:06:00 GMT

You can't explicitly free the message, it's handled automagically when your app quits (and no you can't even free it with GlobalDeleteAtom). And I'm sure there is some refcounting goodness in the object manager to account for multiple processes registering the message. As for what is the merits of atoms... It's just a hash table so I'm sure you mean the global one since that is more interesting. Basically that is mostly good for keeping track of wndclasses, easy way to check if multiple processes are open, or for easy communication between processes. But there are much, much better ways for the latter two.

RE: Which message numbers belong to whom?

Jordan Russell — Wed, 03 Dec 2003 08:34:00 GMT

In my tests, registered messages don't appear to be (completely?) freed when a process terminates. If I register two messages in application, then swap the order in which the messages are registered and run it again, each message gets the same ID as before.

RE: Which message numbers belong to whom?

Anonymous — Wed, 03 Dec 2003 09:18:00 GMT

Eh? That's probably because the string gets hashed to the same numeric value again.

RE: Which message numbers belong to whom?

Jordan Russell — Wed, 03 Dec 2003 11:35:00 GMT

I don't think that's the case. On Windows 2000 and XP, the IDs seem to be assigned sequentially; the content of the string doesn't matter.

RE: Which message numbers belong to whom?

Raymond Chen — Wed, 03 Dec 2003 18:14:00 GMT

Registered window messages cannot be freed; once they've been created they will hang around until you log off. In Windows 3,1/95/98/etc,, the numerical value of a registered window message was based on the address of the hash table entry for the name, so they looked pseudorandom. In Windows NT/2000/XP/etc., the numerical values are sequentially assigned in order of request.

RE: Which message numbers belong to whom?

Jordan Russell — Wed, 03 Dec 2003 20:30:00 GMT

Thanks for the clarification. :)

The bonus window bytes at GWLP_USERDATA

The Old New Thing — Thu, 03 Mar 2005 18:01:00 GMT

A predefined place to hide a pointer-sized value.

Remember what happens when you broadcast a message

The Old New Thing — Sat, 10 Jun 2006 17:00:15 GMT

Most messages are not safe to broadcast.

Remember what happens when you broadcast a message

The Old New Thing — Mon, 12 Jun 2006 17:29:28 GMT

Most messages are not safe to broadcast.

Waiting until the dialog box is displayed before doing something

The Old New Thing — Mon, 25 Sep 2006 17:00:16 GMT

Answer to previous exercise.

When something is available for the user, which user are we talking about?

The Old New Thing — Tue, 10 Oct 2006 17:00:14 GMT

And when something is reserved, who's it reserved for?

If control-specific messages belong to the WM_USER range, why are messages like BM_SETCHECK in the system message range?

Mon, 10 Sep 2007 19:26:48 GMT

PingBack from http://blogs.msdn.com/oldnewthing/archive/2007/09/10/4849069.aspx