[Sbcl-help] warning (cast x c-string)

[Yaroslav K. <kav...@je...>]

foreign function declare as:

(define-alien-routine my-func (* char) ...)

If I compile next code:

(with-alien ((x (* char) (my-func ...)))
   (prog1 (cast x c-string)
     (free-alien x)))

I get warning:

; in: DEFUN MY-FUN2
;     (CAST STR C-STRING)
; --> SB-ALIEN-INTERNALS:%CAST SB-ALIEN-INTERNALS:NATURALIZE IF
; ==>
;   NIL
;
; caught WARNING:
;   The binding of ARRAY is not a STRING:
;     NIL
;   See also:
;     The SBCL Manual, Node "Handling of Types"

I did not declare function as returning c-string because necessary to 
free memory.

Code works but how to avoid the warning?

Thanks!

-- 
WBR, Yaroslav Kavenchuk.