---
name: "XGetEventData"
section: "3"
platform: "linux"
package: "libx11"
version: "1.8.14-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/XGetEventData"
---

# XGetEventData(3)

retrieve and free additional event data through cookies.

## 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)](/XNextEvent/3.md),\
 *Xlib - C Language X Interface*