###### (This is the legacy documentation for stable SDL2, the current stable version; [SDL3](https://wiki.libsdl.org/SDL3/) is the current development version.)
# SDL_SetAssertionHandler

Set an application-defined assertion handler.

## Header File

Defined in [SDL_assert.h](https://github.com/libsdl-org/SDL/blob/SDL2/include/SDL_assert.h)

## Syntax

```c
void SDL_SetAssertionHandler(
                    SDL_AssertionHandler handler,
                    void *userdata);

```

## Function Parameters

|                  |                                                                                                                           |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------- |
| **handler**      | the [SDL_AssertionHandler](SDL_AssertionHandler) function to call when an assertion fails or NULL for the default handler |
| **userdata**     | a pointer that is passed to `handler`                                                                                     |

## Remarks

This function allows an application to show its own assertion UI and/or
force the response to an assertion failure. If the application doesn't
provide this, SDL will try to do the right thing, popping up a
system-specific GUI dialog, and probably minimizing any fullscreen windows.

This callback may fire from any thread, but it runs wrapped in a mutex, so
it will only fire from one thread at a time.

This callback is NOT reset to SDL's internal handler upon
[SDL_Quit](SDL_Quit)()!

## Version

This function is available since SDL 2.0.0.

## See Also

* [SDL_GetAssertionHandler](SDL_GetAssertionHandler)

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[CategoryAPI](CategoryAPI), [CategoryAPIFunction](CategoryAPIFunction)