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