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)))
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