XGetEventData, XFreeEventData, XGenericEventCookie - retrieve and free additional event data through

display   Specifies the connection to the X server.

       cookie    Specifies the cookie to free or retrieve the data for.

       Some extension XGenericEvents require additional memory to store  information.   For  these  events,  the
       library   returns   a   XGenericEventCookie   with   a  token  ('cookie')  unique  to  this  event.   The
       XGenericEventCookie's data pointer is undefined until XGetEventData is called.

       The XGetEventData function retrieves this extra data for the given cookie.  No round-trip to  the  server
       is  required.  If the cookie is invalid or the event is not an event handled by cookie handlers, False is
       returned.  If XGetEventData returns True, the cookie's data pointer points to the memory  containing  the
       event  information.   A client must call XFreeEventData to free this memory.  XGetEventData returns False
       for multiple calls for the same event cookie.

       The XFreeEventData function frees the data associated with a cookie.  A client must  call  XFreeEventData
       for each cookie claimed with XGetEventData.

       XEvent event;
       XGenericEventCookie *cookie = &ev;

       XNextEvent(display, &event);
       if (XGetEventData(display, cookie)) {
           handle_cookie_event(cookie->data);
       } else
           handle_event(&event);
       }
       XFreeEventData(display, cookie);

       XGetEventData,  XFreeEventData,  XGenericEventCookie  -  retrieve  and free additional event data through
       cookies.

       A  cookie  is  defined as unclaimed if it has been returned to the client through XNextEvent but its data
       has not been retrieved via XGetEventData.  Subsequent calls to XNextEvent may free memory associated with
       unclaimed cookies.  Multi-threaded X clients must ensure that XGetEventData is  called  before  the  next
       call to XNextEvent.

XNextEvent(3),
       Xlib-CLanguageXInterface

X Version 11                                      libX11 1.8.12                                 XGetEventData(3)

       typedef struct {
               int type;
               unsigned long serial;
               Bool send_event;
               Display *display;
               int extension;
               int evtype;
               unsigned int cookie;
               void *data;
       } XGenericEventCookie;

       Bool XGetEventData(Display *display, XGenericEventCookie *cookie);

       void XFreeEventData(Display *display, XGenericEventCookie *cookie);