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<html lang="en"><head><title>Using the GNU Compiler Collection (GCC)</title><meta http-equiv="Content-Type" content="text/html"><meta name="description" content="Using the GNU Compiler Collection (GCC)"><meta name="generator" content="makeinfo 4.6"><!--Copyright © 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc. <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below). A copy of the license isincluded in the section entitled "GNU Free Documentation License". <p>(a) The FSF's Front-Cover Text is: <p>A GNU Manual <p>(b) The FSF's Back-Cover Text is: <p>You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.--><meta http-equiv="Content-Style-Type" content="text/css"><style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller }--></style></head><body><div class="node"><p>Node: <a name="Cast%20to%20Union">Cast to Union</a>,Next: <a rel="next" accesskey="n" href="Case-Ranges.html#Case%20Ranges">Case Ranges</a>,Previous: <a rel="previous" accesskey="p" href="Designated-Inits.html#Designated%20Inits">Designated Inits</a>,Up: <a rel="up" accesskey="u" href="C-Extensions.html#C%20Extensions">C Extensions</a><hr><br></div><h3 class="section">Cast to a Union Type</h3><p>A cast to union type is similar to other casts, except that the typespecified is a union type. You can specify the type either with<code>union </code><var>tag</var><code></code> or with a typedef name. A cast to union is actuallya constructor though, not a cast, and hence does not yield an lvalue likenormal casts. (See <a href="Compound-Literals.html#Compound%20Literals">Compound Literals</a>.) <p>The types that may be cast to the union type are those of the membersof the union. Thus, given the following union and variables:<pre class="smallexample"> union foo { int i; double d; }; int x; double y; </pre><p>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 ofunion type is equivalent to storing in a member of the union:<pre class="smallexample"> union foo u; /* <small class="dots">...</small> */ 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); /* <small class="dots">...</small> */ hack ((union foo) x); </pre> </body></html>⌨️ 快捷键说明
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