Sophie: sbcl-1.0.31-1mdv2010.0 i586

sbcl-1.0.31-1mdv2010.0.i586.rpm

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<h4 class="subsection">8.7.1 The <code>alien-funcall</code> Primitive</h4>

<div class="defun">
&mdash; Function: <b>sb-alien:alien-funcall</b><var> alien-function &amp;rest arguments<a name="index-sb_002dalien_003aalien_002dfuncall-300"></a></var><br>
<blockquote><p><a name="index-alien_002dfuncall-301"></a>
The <code>alien-funcall</code> function is the foreign function call
primitive: <var>alien-function</var> is called with the supplied
<var>arguments</var> and its C return value is returned as a Lisp value. 
The <var>alien-function</var> is an arbitrary run-time expression; to refer
to a constant function, use <code>extern-alien</code> or a value defined by
<code>define-alien-routine</code>.

        <p>The type of <code>alien-function</code> must be <code>(alien (function
...))</code>  or <code>(alien (* (function ...)))</code>.  The function type is
used to determine how to call the function (as though it was declared
with a prototype.)  The type need not be known at compile time, but
only known-type calls are efficiently compiled.  Limitations:

          <ul>
<li>Structure type return values are not implemented.

          <li>Passing of structures by value is not implemented.

        </ul>

     </blockquote></div>

   <p>Here is an example which allocates a <code>(struct foo)</code>, calls a
foreign function to initialize it, then returns a Lisp vector of all
the <code>(* (struct foo))</code> objects filled in by the foreign call:

<pre class="lisp">     ;; Allocate a foo on the stack.
     (with-alien ((f (struct foo)))
       ;; Call some C function to fill in foo fields.
       (alien-funcall (extern-alien "mangle_foo" (function void (* foo)))
                      (addr f))
       ;; Find how many foos to use by getting the A field.
       (let* ((num (slot f 'a))
              (result (make-array num)))
         ;; Get a pointer to the array so that we don't have to keep extracting it:
         (with-alien ((a (* (array (* (struct foo)) 100)) (addr (slot f 'b))))
           ;; Loop over the first N elements and stash them in the result vector.
           (dotimes (i num)
             (setf (svref result i) (deref (deref a) i)))
           ;; Voila.
           result)))
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