hpux man page for xifevent

XIfEvent()																XIfEvent()

Name
  XIfEvent - wait for event matched in predicate procedure.

Synopsis
  XIfEvent(display, event_return, predicate, args)
	Display *display;
	XEvent *event_return;
	Bool (*predicate)();
	char *args;

Arguments
  display   Specifies a connection to an X server; returned from XOpenDisplay().

  event_return
	    Returns the matched event.

  predicate Specifies the procedure to be called to determine if the next event satisfies your criteria.

  args	    Specifies the user-specified arguments to be passed to the predicate procedure.

Description
  XIfEvent() checks the event queue for events, uses the user-supplied routine to check if one meets certain criteria, and removes the match-
  ing event from the input queue.  XIfEvent() returns only when the specified predicate procedure returns True for an event.   The  specified
  predicate  is  called  once for each event on the queue until a match is made, and each time an event is added to the queue, with the argu-
  ments display, event_return, and arg.

  If no matching events exist on the queue, XIfEvent() flushes the request buffer and waits for an appropriate event to arrive.  Use  XCheck-
  IfEvent() if you don't want to wait for an event.

  For more information, see Volume One, Chapter 8, Events.

See Also
  XQLength(),	XAllowEvents(),   XCheckIfEvent(),   XCheckMaskEvent(),  XCheckTypedEvent(),  XCheckTypedWindowEvent(),  XCheckWindowEvent(),
  XEventsQueued(), XGetInputFocus(), XGetMotionEvents(), XMaskEvent(),	XNextEvent(),  XPeekEvent(),  XPeekIfEvent(),  XPending(),  XPutBack-
  Event(), XSelectInput(), XSendEvent(), XSetInputFocus(), XSynchronize(), XWindowEvent().

Xlib - Input Handling															XIfEvent()