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<h3 class="section">5.3 Cross-References to Other Types</h3>

<p>A type can be used before it is defined; one common way to deal with
that situation is just to use a type reference to a type which has not
yet been defined.

   <p>Another way is with the &lsquo;<samp><span class="samp">x</span></samp>&rsquo; type descriptor, which is followed by
&lsquo;<samp><span class="samp">s</span></samp>&rsquo; for a structure tag, &lsquo;<samp><span class="samp">u</span></samp>&rsquo; for a union tag, or &lsquo;<samp><span class="samp">e</span></samp>&rsquo; for
a enumerator tag, followed by the name of the tag, followed by &lsquo;<samp><span class="samp">:</span></samp>&rsquo;. 
If the name contains &lsquo;<samp><span class="samp">::</span></samp>&rsquo; between a &lsquo;<samp><span class="samp">&lt;</span></samp>&rsquo; and &lsquo;<samp><span class="samp">&gt;</span></samp>&rsquo; pair (for
C<tt>++</tt> templates), such a &lsquo;<samp><span class="samp">::</span></samp>&rsquo; does not end the name&mdash;only a single
&lsquo;<samp><span class="samp">:</span></samp>&rsquo; ends the name; see <a href="Nested-Symbols.html#Nested-Symbols">Nested Symbols</a>.

   <p>For example, the following C declarations:

<pre class="example">     struct foo;
     struct foo *bar;
</pre>
   <p class="noindent">produce:

<pre class="example">     .stabs "bar:G16=*17=xsfoo:",32,0,0,0
</pre>
   <p>Not all debuggers support the &lsquo;<samp><span class="samp">x</span></samp>&rsquo; type descriptor, so on some
machines GCC does not use it.  I believe that for the above example it
would just emit a reference to type 17 and never define it, but I
haven't verified that.

   <p>Modula-2 imported types, at least on AIX, use the &lsquo;<samp><span class="samp">i</span></samp>&rsquo; type
descriptor, which is followed by the name of the module from which the
type is imported, followed by &lsquo;<samp><span class="samp">:</span></samp>&rsquo;, followed by the name of the
type.  There is then optionally a comma followed by type information for
the type.  This differs from merely naming the type (see <a href="Typedefs.html#Typedefs">Typedefs</a>) in
that it identifies the module; I don't understand whether the name of
the type given here is always just the same as the name we are giving
it, or whether this type descriptor is used with a nameless stab
(see <a href="String-Field.html#String-Field">String Field</a>), or what.  The symbol ends with &lsquo;<samp><span class="samp">;</span></samp>&rsquo;.

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