My C Program provides a callback function for a hook. How can I keep it alive, un-kludgily?

Question

Currently, I'm spawning a message box with a OS-library function (Windows.h), which magically keeps my program alive and responding to calls to the callback function.

What alternative approach could be used to silently let the program run forever?

Trapping 'Ctrl-c' or SIGINT and subsequently calling RemoveHook() for a clean exit would be nice to have but is not essential.

HOOK my_hook;

CALLBACK my_callback_fn()
{
  ...
}

int main()
{
  my_hook = SetHook(my_callback_fn);
  MessageBox("Press OK to stop."); // This is bad.
  RemoveHook(my_hook);
  return 0;
}

Answer 1

A simple solution is to call Sleep() in a loop

int main() {
   // your stuff
   while(1) {
      Sleep( 10000 );
   }
   return 0;
}

but note that if you want to do the remove hook stuff, you will need to do Ctrl-C trapping..

Answer 2

creating windows services with the command line could be a way to go

You could also create it programaticaly

Answer 3

This may sounds weird, but there is a global variable. The clipboard.

You can listen to clipboard modifications by trapping the:

• WM_CHANGECBCHAIN
• WM_DRAWCLIPBOARD

When WM_DRAWCLIPBOARD is sent, you read the clipboard text and if it starts with your "magic" word, ie "##EXIT##", you can terminate your application.

Answer 4

You probably want to pump messages. A typical message loop looks like something like this:

BOOl ret;
MSG msg;
while ((ret=::GetMessage(&msg, hWnd, 0, 0))!=0)
{
  ::TranslateMessage(&msg);
  ::DispatchMessage(&msg);
}

You don't seem to have an actual window to pump on, and you don't say what SetHook is actually doing - maybe that will be able to provide one for you?

Another method is to use the MsgWait functions. Maybe you have some kind of handle that you are waiting to become signalled so you can exit?:

while (::MsgWaitForMultipleObjects(1, &handle, FALSE, INFINITE, QS_ALLEVENTS)==WAIT_OBJECT_0+1+
{
  BOOl ret;
  MSG msg;
  while ((ret=::PeekMessage(&msg, hWnd, 0, 0, TRUE))!=0)
  {
    ::TranslateMessage(&msg);
    ::DispatchMessage(&msg);
  }
}