CFFI User Manual - Common Lisp.net

Chapter 6: Foreign Types 34
;; Initialize the slots
(setf (foreign-slot-value ptr ’point ’x) 42
(foreign-slot-value ptr ’point ’y) 42)
;; Return a list with the coordinates
(with-foreign-slots ((x y) ptr point)
(list x y)))
⇒ (42 42)
;; Using the :size and :offset options to define a partial structure.
;; (this is useful when you are interested in only a few slots
;; of a big foreign structure)
(defcstruct (foo :size 32)
"Some struct with 32 bytes."
;
(x :int :offset 16) ; an int at offset 16
(y :int) ; another int at offset 16+sizeof(int)
;
(z :char :offset 24)) ; a char at offset 24
;
CFFI> (foreign-type-size ’foo)
⇒ 32
;;; Using :count to define arrays inside of a struct.
(defcstruct video_tuner
(name :char :count 32))
See Also
[foreign-slot-pointer], page 46
[foreign-slot-value], page 47
[with-foreign-slots], page 55