Re: [Chicken-users] Making stack-allocated Chicken-managed objects from C

[Jim Ursetto]

On Mar 6, 2012, at 10:31 AM, Kristian Lein-Mathisen wrote:

(define %make-point (foreign-primitive void
                                       (((c-pointer (struct point)) dest) (float x) (float y))
#<<END
dest->x = x;
dest->y = y;
C_return();
END
))

(define (make-point x y) 
        (let ((loc (location (make-blob %get struct-size somehow%))))
           (%make-point loc x y)
            loc))

%get struct-size somehow%

 -> (foreign-value "sizeof(struct point)" int)

Avoid the locative by using scheme-pointer instead of c-pointer.

There's no reason I can think of to use foreign-primitive there instead of foreign-lambda*.

Ideally wrap the blob in a define-record for safety issues (not done below,

we stick with a bare pointer as in your example).

Code:

#>

struct point { float x; float y; };

<#

(define %make-point (foreign-lambda* void

                        ((scheme-pointer b) (float x) (float y))

#<<END

((struct point *)b)->x = x;

((struct point *)b)->y = y;

END

))

(define (make-point x y)

  (let ((b (make-blob (foreign-value "sizeof(struct point)" int))))

    (%make-point b x y)

    b))

(define point-y (foreign-lambda* float ((scheme-pointer b))

                 "return(((struct point *)b)->y);"))

(print (point-y (make-point 1.5 2.5)))