XGetEventData(3)

1XGetEventData(3)                XLIB FUNCTIONS                XGetEventData(3)
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NAME

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

10       Bool XGetEventData(Display *display, XGenericEventCookie *cookie);
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12       void XFreeEventData(Display *display, XGenericEventCookie *cookie);
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ARGUMENTS

17       display   Specifies the connection to the X server.
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19       cookie    Specifies the cookie to free or retrieve the data for.
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STRUCTURES

23       typedef struct {
24            int type;
25            unsigned long serial;
26            Bool send_event;
27            Display *display;
28            int extension;
29            int evtype;
30            unsigned int cookie;
31            void *data;
32       } XGenericEventCookie;
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DESCRIPTION

36       Some extension XGenericEvents require additional memory to store infor‐
37       mation.  For these events, the library returns a XGenericEventCookie
38       with a token ('cookie') unique to this event. The XGenericEventCookie's
39       data pointer is undefined until XGetEventData is called.
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41       The XGetEventData function retrieves this extra data for the given
42       cookie. No round-trip to the server is required. If the cookie is
43       invalid or the event is not an event handled by cookie handlers, False
44       is returned. If XGetEventData returns True, the cookie's data pointer
45       points to the memory containing the event information. A client must
46       call XFreeEventData to free this memory.  XGetEventData returns False
47       for multiple calls for the same event cookie.
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49       The XFreeEventData function frees the data associated with a cookie. A
50       client must call XFreeEventData for each cookie claimed with XGetEvent‐
51       Data.
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EXAMPLE CODE

55       XEvent event;
56       XGenericEventCookie *cookie = &ev;
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58       XNextEvent(display, &event);
59       if (XGetEventData(display, cookie)) {
60           handle_cookie_event(cookie->data);
61       } else
62           handle_event(&event);
63       }
64       XFreeEventData(display, cookie);
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NOTES

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