[Chicken-users] Check for NULL struct

[Cosme Enmanuel Zamudio Salazar]

Is there a way to check for a NULL structure returned from a C function?

this is the structure

(define-record sdl-surface pointer)

(define-record-printer (sdl-surface s out)

  (for-each (lambda (x) (display x out))

   (list "#<sdl-surface "(sdl-surface-pointer s)">")))

(define-foreign-type SDL_Surface (c-pointer "SDL_Surface")

  sdl-surface-pointer

  make-sdl-surface)

the NULL can be returned when i try to load an image that doesnt exists:

#;12> (img-load "test.png")

#<sdl-surface #f>

but how do i check if its NULL ?

Thanks :)