Re: Accessing elements in foreign array of structs

Sorry spam (original reply didn’t include the mailing list), but does 
something like this work?

(use-package "FLI")

(define-c-struct (point (:foreign-name "tagPOINT"))
   (x :long)
   (y :long))

(with-dynamic-foreign-objects ((points point :nelems 3))
   (let ((current (copy-pointer points)))
     (dotimes (index 3)
       (setf (foreign-slot-value current 'x :object-type 'point) index
             (foreign-slot-value current 'y :object-type 'point) index)
       (format t "~S: ~S ~S,~S~%"
               index
               current
               (foreign-slot-value current 'x)
               (foreign-slot-value current 'y))
       (incf-pointer current))))

The compiler can optimise slot access if you pass the :object-type, but 
it’s not strictly necessary.

Julian.


------ Original Message ------
>From "Erik Ronström (as erik dot ronstrom at doremir dot com)" 
<[email protected]>
To "LispWorks" <[email protected]>
Date 13/4/2026 4:53:18 am
Subject Accessing elements in foreign array of structs

>Hi,
>
>I am calling a foreign function that takes an array of points as input.
>
>(fli:define-c-struct (point (:foreign-name "tagPOINT"))
>   (x :long)
>   (y :long))
>
>(let ((points (fli:allocate-foreign-object :type 'point :nelems 3)))
>
>   (the-foreign-function points))
>
>
>I can't figure out how to access the elements of the foreign array directly.
>
>This works:
>
>(let ((p (fli:allocate-foreign-object :type 'point)))
>   (setf (fli:foreign-slot-value p 'x) 100
>         (fli:foreign-slot-value p 'y) 200
>         (fli:dereference points :index 0) p)
>
>But how do I set the elements of points without using an intermediate object?
>
>Erik
>
>
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