> Is it possible to share/send a stream with a foreign function?  I
> would like to have with-open-file open a file, then give the stream
> (or some mapping of that stream) to a C function that expects a (C)
> stream (e.g., something that would result from the C function fopen).
> This C function would put output to that stream and then return to the 
> calling CL function.

Here's what I've been using to do just that.  So far I haven't had any trouble 
with it, but I make no guarantees.  The basic ideas is to flush out all pending 
output to the stream, get its file descriptor, duplicate it, open it as a stdio 
stream, do the I/O, and close the stream.

Rob Malouf
<stanford.edu at malouf>
======================================

(ff:defforeign-list 
    '((dup
       :arguments (integer)
       :return-type :integer
       :unconverted-entry-name "dup")
      (fdopen
       :arguments (integer string)
       :return-type :integer
       :unconverted-entry-name "fdopen")
      (fclose
       :arguments (integer)
       :return-type :void
       :unconverted-entry-name "fclose")
      (c-image-gif 
       :arguments (integer integer)
       :return-type :void
       :unconverted-entry-name "gdImageGif")))

(defun image-gif (image stream)
  (force-output stream)
  (let* ((fd (dup (excl:stream-output-fn stream)))
	 (out (fdopen fd "w")))
    (c-image-gif image out)
    (fclose out)))