###### (This is the documentation for SDL3, which is under heavy development and the API is changing! [SDL2](https://wiki.libsdl.org/SDL2/) is the current stable version!)
# SDL_AddEventWatch

Add a callback to be triggered when an event is added to the event queue.

## Header File

Defined in [SDL_events.h](https://github.com/libsdl-org/SDL/blob/main/include/SDL3/SDL_events.h), but apps should use `#include <SDL3/SDL.h>`

## Syntax

```c
int SDL_AddEventWatch(SDL_EventFilter filter, void *userdata);

```

## Function Parameters

|                  |                                                                               |
| ---------------- | ----------------------------------------------------------------------------- |
| **filter**       | an [SDL_EventFilter](SDL_EventFilter) function to call when an event happens. |
| **userdata**     | a pointer that is passed to `filter`                                          |

## Return Value

Returns 0 on success, or a negative error code on failure; call
[SDL_GetError](SDL_GetError)() for more information.

## Remarks

`filter` will be called when an event happens, and its return value is
ignored.

**WARNING**: Be very careful of what you do in the event filter function,
as it may run in a different thread!

If the quit event is generated by a signal (e.g. SIGINT), it will bypass
the internal queue and be delivered to the watch callback immediately, and
arrive at the next event poll.

Note: the callback is called for events posted by the user through
[SDL_PushEvent](SDL_PushEvent)(), but not for disabled events, nor for
events by a filter callback set with
[SDL_SetEventFilter](SDL_SetEventFilter)(), nor for events posted by the
user through [SDL_PeepEvents](SDL_PeepEvents)().

## Version

This function is available since SDL 3.0.0.

## See Also

* [SDL_DelEventWatch](SDL_DelEventWatch)
* [SDL_SetEventFilter](SDL_SetEventFilter)

----
[CategoryAPI](CategoryAPI), [CategoryAPIFunction](CategoryAPIFunction), [CategoryEvents](CategoryEvents)