alien-funcall PrimitiveThe
alien-funcallfunction is the foreign function call primitive: alien-function is called with the supplied arguments and its C return value is returned as a Lisp value. The alien-function is an arbitrary run-time expression; to refer to a constant function, useextern-alienor a value defined bydefine-alien-routine.The type of
alien-functionmust be(alien (function ...))or(alien (* (function ...))). The function type is used to determine how to call the function (as though it was declared with a prototype.) The type need not be known at compile time, but only known-type calls are efficiently compiled. Limitations:
- Structure type return values are not implemented.
- Passing of structures by value is not implemented.
Here is an example which allocates a (struct foo), calls a
foreign function to initialize it, then returns a Lisp vector of all
the (* (struct foo)) objects filled in by the foreign call:
;; Allocate a foo on the stack.
(with-alien ((f (struct foo)))
;; Call some C function to fill in foo fields.
(alien-funcall (extern-alien "mangle_foo" (function void (* foo)))
(addr f))
;; Find how many foos to use by getting the A field.
(let* ((num (slot f 'a))
(result (make-array num)))
;; Get a pointer to the array so that we don't have to keep extracting it:
(with-alien ((a (* (array (* (struct foo)) 100)) (addr (slot f 'b))))
;; Loop over the first N elements and stash them in the result vector.
(dotimes (i num)
(setf (svref result i) (deref (deref a) i)))
;; Voila.
result)))