hpux man page for xcheckifevent

XCheckIfEvent() 														   XCheckIfEvent()

Name
  XCheckIfEvent - check the event queue for a matching event; don't wait.

Synopsis
  Bool XCheckIfEvent(display, event_return, predicate, arg)
	Display *display;
	XEvent *event_return;
	Bool (*predicate)();
	char *arg;

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

  event_return
	    Returns the matched event structure.

  predicate Specifies the procedure that is called to determine if the next event in the queue matches your criteria.

  arg	    Specifies the user-specified argument that will be passed to the predicate procedure.

Returns
  True if a matching event is found, else False.

Description
  XCheckIfEvent()  returns the next event in the queue that is matched by the specified predicate procedure.  If found, that event is removed
  from the queue, its structure is copied into the client-supplied XEvent, and True is returned.   If  no  match  is  found,  XCheckIfEvent()
  returns False and flushes the request buffer.  No other events are removed from the queue.  Later events in the queue are not searched.

  The predicate procedure is called with the arguments display, event, and arg.

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

See Also
  XQLength(),  XAllowEvents(),	XCheckMaskEvent(),  XCheckTypedEvent(), XCheckTypedWindowEvent(), XCheckWindowEvent(), XEventsQueued(), XGet-
  InputFocus(), XGetMotionEvents(), XIfEvent(), XMaskEvent(), XNextEvent(), XPeekEvent(), XPeekIfEvent(), XPending(),  XPutBackEvent(),  XSe-
  lectInput(), XSendEvent(), XSetInputFocus(), XSynchronize(), XWindowEvent().

Xlib - Input Handling														   XCheckIfEvent()