Sophie: sbcl-1.0.31-1mdv2010.0 i586

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

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<h3 class="section">8.5 Foreign Data Structure Examples</h3>

<!-- AKA "Alien Data Structure Example" in the CMU CL manual -->
<p>Now that we have alien types, operations and variables, we can
manipulate foreign data structures.  This C declaration

<pre class="example">     struct foo {
         int a;
         struct foo *b[100];
     };
</pre>
   <p>can be translated into the following alien type:

<pre class="lisp">     (define-alien-type nil
       (struct foo
         (a int)
         (b (array (* (struct foo)) 100))))
</pre>
   <p>Once the <code>foo</code> alien type has been defined as above, the C
expression

<pre class="example">     struct foo f;
     f.b[7].a;
</pre>
   <p>can be translated in this way:

<pre class="lisp">     (with-alien ((f (struct foo)))
       (slot (deref (slot f 'b) 7) 'a)
       ;;
       ;; Do something with f...
       )
</pre>
   <p>Or consider this example of an external C variable and some accesses:

<pre class="example">     struct c_struct {
             short x, y;
             char a, b;
             int z;
             c_struct *n;
     };
     extern struct c_struct *my_struct;
     my_struct-&gt;x++;
     my_struct-&gt;a = 5;
     my_struct = my_struct-&gt;n;
</pre>
   <p>which can be manipulated in Lisp like this:

<pre class="lisp">     (define-alien-type nil
       (struct c-struct
               (x short)
               (y short)
               (a char)
               (b char)
               (z int)
               (n (* c-struct))))
     (define-alien-variable "my_struct" (* c-struct))
     (incf (slot my-struct 'x))
     (setf (slot my-struct 'a) 5)
     (setq my-struct (slot my-struct 'n))
</pre>
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