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| <title>Using the GNU Compiler Collection (GCC): Cast to Union</title> |
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| <a name="Cast-to-a-Union-Type"></a> |
| <h3 class="section">6.28 Cast to a Union Type</h3> |
| <a name="index-cast-to-a-union"></a> |
| <a name="index-union_002c-casting-to-a"></a> |
| |
| <p>A cast to union type is similar to other casts, except that the type |
| specified is a union type. You can specify the type either with |
| <code>union <var>tag</var></code> or with a typedef name. A cast to union is actually |
| a constructor, not a cast, and hence does not yield an lvalue like |
| normal casts. (See <a href="Compound-Literals.html#Compound-Literals">Compound Literals</a>.) |
| </p> |
| <p>The types that may be cast to the union type are those of the members |
| of the union. Thus, given the following union and variables: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">union foo { int i; double d; }; |
| int x; |
| double y; |
| </pre></div> |
| |
| <p>both <code>x</code> and <code>y</code> can be cast to type <code>union foo</code>. |
| </p> |
| <p>Using the cast as the right-hand side of an assignment to a variable of |
| union type is equivalent to storing in a member of the union: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">union foo u; |
| /* <span class="roman">…</span> */ |
| u = (union foo) x ≡ u.i = x |
| u = (union foo) y ≡ u.d = y |
| </pre></div> |
| |
| <p>You can also use the union cast as a function argument: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">void hack (union foo); |
| /* <span class="roman">…</span> */ |
| hack ((union foo) x); |
| </pre></div> |
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