<html> <head> <meta content="text/html; charset=UTF-8" http-equiv="Content-Type"> </head> <body bgcolor="#FFFFFF" text="#000000"> <div class="moz-cite-prefix">Hi, Version with conversion to/from string: <tt> (define (_string/locale/len n) ; n - bytes, not characters </tt><tt> </tt><tt> (make-ctype (make-array-type _byte n) </tt><tt> </tt><tt> ;->C </tt><tt> </tt><tt> (lambda (in) </tt><tt> </tt><tt> (cond </tt><tt> </tt><tt> [(not in) </tt><tt> </tt><tt> (make-bytes n)] </tt><tt> </tt><tt> [(string? in) </tt><tt> </tt><tt> (define bs (string->bytes/locale in)) </tt><tt> </tt><tt> (cond </tt><tt> </tt><tt> [((bytes-length bs) . >= . n) ; len+1 > n </tt><tt> </tt><tt> (error '_string/locale/len "string is too long\n~v" in)] </tt><tt> </tt><tt> [else </tt><tt> </tt><tt> (define out (make-bytes n)) </tt><tt> </tt><tt> (bytes-copy! out 0 bs) </tt><tt> </tt><tt> out])] </tt><tt> </tt><tt> [else </tt><tt> </tt><tt> (error '_string/locale/len "expected string? or #f, got ~v" in)])) </tt><tt> </tt><tt> ;->racket </tt><tt> </tt><tt> (lambda (in) </tt><tt> </tt><tt> (define bs (make-sized-byte-string in n)) </tt><tt> </tt><tt> (define len </tt><tt> </tt><tt> (for/fold ([acc 0]) </tt><tt> </tt><tt> ([b (in-bytes bs)] </tt><tt> </tt><tt> [pos (in-naturals)] </tt><tt> </tt><tt> #:final (zero? b)) </tt><tt> </tt><tt> pos)) </tt><tt> </tt><tt> (define sub-bs (subbytes bs 0 len)) </tt><tt> </tt><tt> (bytes->string/locale sub-bs))))</tt> I would use this: <pre wrap="">(define camera-text-size (* 32 1024)) (define-cstruct _CameraText ([value (_string/locale/len camera-text-size)]))</pre> For passing as a parameter to 'gp_camera_get_about': <tt>(define cam-text (make-CameraText #f))</tt> 13.11.2014 20:00, Bartosz Przygoda пишет: </div> <blockquote cite="mid:CADV3fd2hB-LhBNjjEzD4boNa1E958NHB9nUxRA3oa7aLLTiJYg@mail.gmail.com" type="cite"> <pre wrap="">Hello, I'm trying to make racket bindings for libgphoto2. Its API uses CameraText struct for outputting strings, which just wraps char array. My first attempt was: (define _Camera-ptr (_cpointer 'Camera)) (define _CameraText-ptr (_cpointer 'CameraText)) (define-gphoto gp_camera_get_about (_fun _Camera-ptr (v : _CameraText-ptr) _GPContext-ptr -> _int)) But this was giving me segfaults (not to mention the pointer here is opaque and there are no getter functions in API). Later on I've stumbled across <a class="moz-txt-link-freetext" href="https://github.com/dyoo/ffi-tutorial/blob/master/ffi/tutorial/examples/struct-with-array/struct-with-array.rkt">https://github.com/dyoo/ffi-tutorial/blob/master/ffi/tutorial/examples/struct-with-array/struct-with-array.rkt</a> so I've tried this: (define _Camera-ptr (_cpointer 'Camera)) (define camera-text-size (* 32 1024)) (define-cstruct _CameraText ([text (_bytes/len (camera-text-size))])) (define-gphoto gp_camera_get_about (_fun _Camera-ptr (v : _CameraText-pointer) _GPContext-ptr -> _int)) (Where bytes/len is helper taken from that example) How can I initialize this struct to mimic C CameraText txt;? Is there some better way to handle char arrays (and converting them to strings) than _byte array? Or should I go with something like (but this was segfaulting as well): (define-cstruct _CameraText ([text _string])) </pre> <fieldset class="mimeAttachmentHeader"></fieldset> <pre wrap="">____________________ Racket Users list: <a class="moz-txt-link-freetext" href="http://lists.racket-lang.org/users">http://lists.racket-lang.org/users</a> </pre> </blockquote> </body> </html>