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| <h3 class="section">6.27 Cast to a Union Type</h3> |
| |
| <p><a name="index-cast-to-a-union-2327"></a><a name="index-union_002c-casting-to-a-2328"></a> |
| 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 </code><var>tag</var> or with a typedef name. A cast to union is actually |
| a constructor though, 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>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: |
| |
| <pre class="smallexample"> union foo { int i; double d; }; |
| int x; |
| double y; |
| </pre> |
| <p class="noindent">both <code>x</code> and <code>y</code> can be cast to type <code>union foo</code>. |
| |
| <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: |
| |
| <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> |
| <p>You can also use the union cast as a function argument: |
| |
| <pre class="smallexample"> void hack (union foo); |
| /* <span class="roman">...</span> */ |
| hack ((union foo) x); |
| </pre> |
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