Re: [Chicken-users] Re: Structs

[Peter Keller]

On Mon, Oct 14, 2002 at 10:38:40AM -0500, Peter Keller wrote:
> On Mon, Oct 14, 2002 at 08:57:05AM +0200, Felix Winkelmann wrote:
> > In this case I would create a number of foreign-lambda*s
> > that access the slots:
> 
> So, I actually thought of this, but rejected it because I didn't
> understand how gc would affect it. I thought that I could end up with a
> way that I'd have a valid z_stream object with a member field pointing
> to gc'ed data.

So, I tried this out:

(declare
        (foreign_declare #<< EOF
#include <zlib.h>)
EOF
))

(define-foreign-type z_stream (pointer "z_stream"))

(define make-z_stream
    (let (  (alloc (foreign-lambda* z_stream ()
                        "return (malloc(sizeof(z_stream)));"))
            (dealloc (foreign-lambda void "free" c-pointer)))
        (lambda ()
            (let ((m (alloc)))
                (set-finalizer! m dealloc)
                m))))

(define z_stream-next_in
   (foreign-lambda* c-pointer ((z_stream p))
     "return(p->next_in);") )

(define z_stream-next_in-set!
   (foreign-lambda* void ((z_stream p) (u8vector x))
     "p->next_in = x;") )

(let ((foo (make-z_stream)))
    (z_stream-next_in-set! foo (u8vector 1 2 3 4 5))
    (print (z_stream-next_in foo)))

And this was the output:
#<pointer -1073745280.>

I seem to have lost the knowledge that next_in was a u8vector.

-pete