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| <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’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 "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;", |
| 128,0,0,0 |
| </pre></div> |
| |
| <p>The symbol descriptor ‘<samp>T</samp>’, following the ‘<samp>name:</samp>’ means that |
| the stab describes an enumeration, structure, or union tag. The type |
| descriptor ‘<samp>u</samp>’, following the ‘<samp>23=</samp>’ of the type definition, |
| narrows it down to a union type definition. Following the ‘<samp>u</samp>’ is |
| the number of bytes in the union. After that is a list of union element |
| descriptions. Their format is ‘<samp><var>name</var>:<var>type</var>, <var>bit |
| offset into the union</var>, <var>number of bytes for the element</var>;</samp>’. |
| </p> |
| <p>The stab for the union variable is: |
| </p> |
| <div class="example"> |
| <pre class="example">.stabs "an_u:23",128,0,0,-20 # <span class="roman">128 is N_LSYM</span> |
| </pre></div> |
| |
| <p>‘<samp>-20</samp>’ specifies where the variable is stored (see <a href="Stack-Variables.html#Stack-Variables">Stack Variables</a>). |
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