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<h3 class="section">6.29 Cast to a Union Type</h3>
<p><a name="index-cast-to-a-union-3029"></a><a name="index-union_002c-casting-to-a-3030"></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, 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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