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<a name="Unions"></a>
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<hr>
<a name="Unions-1"></a>
<h3 class="section">5.10 Unions</h3>

<div class="example">
<pre class="example">union u_tag {
  int  u_int;
  float u_float;
  char* u_char;
} an_u;
</pre></div>

<p>This code generates a stab for a union tag and a stab for a union
variable.  Both use the <code>N_LSYM</code> stab type.  If a union variable is
scoped locally to the procedure in which it is defined, its stab is
located immediately preceding the <code>N_LBRAC</code> for the procedure&rsquo;s block
start.
</p>
<p>The stab for the union tag, however, is located preceding the code for
the procedure in which it is defined.  The stab type is <code>N_LSYM</code>.  This
would seem to imply that the union type is file scope, like the struct
type <code>s_tag</code>.  This is not true.  The contents and position of the stab
for <code>u_type</code> do not convey any information about its procedure local
scope.
</p>
<div class="smallexample">
<pre class="smallexample"># <span class="roman">128 is N_LSYM</span>
.stabs &quot;u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;&quot;,
       128,0,0,0
</pre></div>

<p>The symbol descriptor &lsquo;<samp>T</samp>&rsquo;, following the &lsquo;<samp>name:</samp>&rsquo; means that
the stab describes an enumeration, structure, or union tag.  The type
descriptor &lsquo;<samp>u</samp>&rsquo;, following the &lsquo;<samp>23=</samp>&rsquo; of the type definition,
narrows it down to a union type definition.  Following the &lsquo;<samp>u</samp>&rsquo; is
the number of bytes in the union.  After that is a list of union element
descriptions.  Their format is &lsquo;<samp><var>name</var>:<var>type</var>, <var>bit
offset into the union</var>, <var>number of bytes for the element</var>;</samp>&rsquo;.
</p>
<p>The stab for the union variable is:
</p>
<div class="example">
<pre class="example">.stabs &quot;an_u:23&quot;,128,0,0,-20     # <span class="roman">128 is N_LSYM</span>
</pre></div>

<p>&lsquo;<samp>-20</samp>&rsquo; specifies where the variable is stored (see <a href="Stack-Variables.html#Stack-Variables">Stack Variables</a>).
</p>


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