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<h3 class="section">5.10 Unions</h3>

<pre class="example">     union u_tag {
       int  u_int;
       float u_float;
       char* u_char;
     } an_u;
</pre>
   <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's block
start.

   <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.

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<pre class="smallexample">     # <span class="roman">128 is N_LSYM</span>
     .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
            128,0,0,0
</pre>
   <p>The symbol descriptor &lsquo;<samp><span class="samp">T</span></samp>&rsquo;, following the &lsquo;<samp><span class="samp">name:</span></samp>&rsquo; means that
the stab describes an enumeration, structure, or union tag.  The type
descriptor &lsquo;<samp><span class="samp">u</span></samp>&rsquo;, following the &lsquo;<samp><span class="samp">23=</span></samp>&rsquo; of the type definition,
narrows it down to a union type definition.  Following the &lsquo;<samp><span class="samp">u</span></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><span class="samp">:</span><var>type</var><span class="samp">, </span><var>bit
offset into the union</var><span class="samp">, </span><var>number of bytes for the element</var><span class="samp">;</span></samp>&rsquo;.

   <p>The stab for the union variable is:

<pre class="example">     .stabs "an_u:23",128,0,0,-20     # <span class="roman">128 is N_LSYM</span>
</pre>
   <p>&lsquo;<samp><span class="samp">-20</span></samp>&rsquo; specifies where the variable is stored (see <a href="Stack-Variables.html#Stack-Variables">Stack Variables</a>).

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