Handling Messages in Console Apps/DLLs in C++ Win32

Question

I would like to have the ability to process Win32 messages in a console app and/or inside a standalone DLL.

I have been able to do it in .NET with the following article and it works great in C# inside a console app and standalone DLL
http://msdn.microsoft.com/en-us/magazine/cc163417.aspx

Is there a way to do the equivalent with C/C++ Win32 APIs? I have tried doing RegisterClassEx(...) and CreateWindow(...) even passing in HWND_MESSAGE to hWndParent but the trouble is that after the "invisible" window is created messages are not being processed probably due to the lack of a message pump.

Where would the message pump go if you had a DLL entry point? I have tried creating another thread in a DLL and put while(GetMesage(..)) there but that did not work either.

Any ideas?

Did you put the message pump on the same thread as your CreateWindow call? — Gabe, Apr 24 '10 at 21:23
Just curious, What kind of Win32 messages do you need from a Console App ? — Romain Hippeau, Apr 25 '10 at 05:03
@Gabe I did not try doing that, will try that next @Romain I am trying to pick up WM_DEVICECHANGE messages after calling RegisterDeviceNotification. — Vicken Simonian, Apr 25 '10 at 23:59
Thanks Gabe. That was it WM_DEVICECHANGE messages are now coming through! — Vicken Simonian, Apr 26 '10 at 06:11

score 2 · Accepted Answer · answered Apr 24 '10 at 21:19

2

You need a message pump yes. The window also has thread affinity so it needs to be created on the same thread that you're running the message pump on. The basic approach is sound, if you include more code it may become clear what the problem is.

answered Apr 24 '10 at 21:19

Logan Capaldo

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score 2 · Answer 2 · edited May 23 '17 at 12:02

In addition to what Logan Capaldo said, you also have the problem that, as a DLL, you don't know at compile time what kind of process is going to be loading you at runtime.

If you are being loaded by a console application (/SUBSYSTEM:CONSOLE), then creating a hidden window of your own and setting up a message pump on that same thread will work fine (as long as you are the first window created).
If you are being loaded by a windows app (/SUBSYSTEM:WINDOWS) then you might run into problems getting messages. They will be sent to the top-level window in the hierarchy, which you didn't create. You'll need to get the hWnd of the main process and subclass it (if you aren't already).
If you are being loaded by a service, then you aren't going to get window messages at all. You instead need to use the RegisterServiceCtrlHandlerEx Function

Handling Messages in Console Apps/DLLs in C++ Win32

2 Answers2