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XGetEventData(3)                XLIB FUNCTIONS                XGetEventData(3)

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

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

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

ARGUMENTS
       display   Specifies the connection to the X server.

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

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

DESCRIPTION
       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.

EXAMPLE CODE
       XEvent event;
       XGenericEventCookie *cookie = &ev;

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

NOTES
       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.

SEE ALSO
       XNextEvent(3),
       Xlib - C Language X Interface

X Version 11                     libX11 1.8.6                 XGetEventData(3)