Creating custom message types in win32?

Question

Is there a way to define and send custom message types in Win32, to be caught by your Main message handler? For example, my main message handler captures messages such as WM_PAINT, WM_RESIZE, WM_LBUTTONDOWN etc. Can I create my own WM_DOSOMETHING? If so, how would I send this message?

Ah, I actually just discovered this was asked before here, however, it doesn't answer how I would actually send this message.

Answer 1

Yes. Just declare a constant in the WM_USER range e.g.

#define WM_RETICULATE_SPLINES (WM_USER + 0x0001)

You can also register a message by name using the RegisterWindowMessage API.

You can then send these messages using SendMessage, PostMessage or any of their variants.

Answer 2

Woah, let's just stop and think here...

First of all, Windows itself sends messages in the WM_USER+n range, that's why WM_APP was invented (I found this out the hard way). But it gets worse... there's nothing to stop badly behaved applications broadcasting WM_USER+n or WM_APP+n messages, and because human beings stole the crystal of infinite stupidity from the Gods, this does indeed happen in the real world.

So, repeat after me, the only safe message is one I define myself and can only see myself. Use RegisterWindowMessage. And even then, be untrusting. When I need a string to define a RegisterWindowMessage, I use GUIDGEN to create the string and put a human-readable app-specific prefix on the resulting gobbledygook to help me differentiate multiple messages in the code.

Bet on the stupidity of your fellow humans - it's always a winning bet.

If you want authoritative background on this whole topic, see here. No that's not my website, it's Joe Newcomer's.

Answer 3

• If you created the window class, you can use the WM_USER range (or WM_APP)
• If it is not your class, you can use WM_APP
• If you want to broadcast the message to every top level window, register your own global message with RegisterWindowMessage