Capturing keyboard input without focus on the programwindow

I am doing a VoIP client and I want to start/stop on WM_KEYDOWN and WM_KEYUP messages for a certain input, say K. When the main window has focus, this is np, but how do I enable it outside of the window? For example, if the window is not in focus and I'm just looking at the desktop or am in a videogame. How does one perform something like this? I am not sure where to begin.

Also -- I guess you somehow has to poll every in开发者_开发百科put even outside the program, is that expensive?

win32 c++ btw

You need to install keyboard hooks: http://msdn.microsoft.com/en-us/library/ms644990(v=VS.85).aspx

This can be very troubling though for every running application if something steals its keyboard messages.

I don't think you want this - if I'm typing a document into Word and I hit K, I'm going to be very angry when your application pops up instead of a "k" appearing in my document.

Windows allows you to assign shortcut keys to an icon on the desktop, but it limits them to the function keys or to combinations containing both Alt and Ctrl. Right-click on a desktop icon and go to Properties, and look for the field marked "Shortcut key".