FFI questions

[Jan Synacek <jsynacek@redhat.com>]

Hello,

Currently I have something like this:

(define libxcb (dynamic-link "libxcb"))

...

(define c-change-window-attributes
  (pointer->procedure void
     (dynamic-func "xcb_change_window_attributes" libxcb)
     (list '* uint32 uint32 '*)))

(define (change-window-attributes conn win mask vals)
   (c-change-window-attributes conn win mask (bytevector->pointer vals)))

The last argument to xcb_change_window_attributes is 'const void *' and I
need to pass a u32 vector to it. As it is right now, it segfaults when I
try passing #u32(something) to 'change-window-attributes'. Is it possible
to make it accept a u32 vector using just Scheme or do I have to work
around it on the C level?


My second question is about FFI and structs. Is it possible to access C
struct members from Scheme by name? If not, how do I generally approach the
problem? I've checked how guile-xcb does it and it seems to be building
hash tables with field names as keys. But that basically requires me to
"redefine" all the C structs that I would be interested in at the Scheme
level.

Regards,
-- 
Jan Synacek
Software Engineer, Red Hat