XGetEventData(3)

okay bestie, welcome to XGetEventData(3) — straight from XLIB FUNCTIONS — the page where cookies are not snacks (well, kinda) and event data gets claimed and freed with main-character precision 💅✨

🎀 NAME 🎀

XGetEventData, XFreeEventData, XGenericEventCookie — retrieve and free additional event data through cookies. That's the whole vibe: extra event data goes in and out via cookies 🍪.

✨ SYNTAX ✨

These signatures are literal, okay? Keep them exactly like this:

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

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

🫶 ARGUMENTS 🫶

• display — specifies the connection to the X server. Your whole X-server link-up, periodt.
• cookie — specifies the cookie to free or retrieve the data for. The little event-data token in question 🍪.

🧚 STRUCTURES 🧚

Here's the XGenericEventCookie struct, copied exactly because we do not mess with code:

       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. No cap.

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. So don't try to double-dip, bestie 💀.

The XFreeEventData function frees the data associated with a cookie. A client must call XFreeEventData for each cookie claimed with XGetEventData. Every claimed cookie gets its cleanup moment, okay? 🫶

🌈 EXAMPLE CODE 🌈

Here's the example block exactly as it appears — code stays code, bestie:

       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.

⚠️ bestie, listen: 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. That's the whole safety vibe check 🔥.

👑 SEE ALSO 👑

• XNextEvent(3)
• Xlib - C Language X Interface

---

signing off with X Version 11, libX11 1.8.14, and the XGetEventData(3) footer label — source, version, and footer tag all accounted for, bestie 💖🎀