📄 cast-to-union.html

📁 gcc手册
💻 HTML
字号:
<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 4.3">

<link href="http://www.gnu.org/software/texinfo/" rel="generator-home">

<!--

Copyright &copy; 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,

1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.



   <p>Permission is granted to copy, distribute and/or modify this document

under the terms of the GNU Free Documentation License, Version 1.2 or

any later version published by the Free Software Foundation; with the

Invariant Sections being "GNU General Public License" and "Funding

Free Software", the Front-Cover texts being (a) (see below), and with

the Back-Cover Texts being (b) (see below).  A copy of the license is

included 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.-->

</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 type

specified 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 actually

a constructor though, not a cast, and hence does not yield an lvalue like

normal 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 members

of the union.  Thus, given the following union and variables:



<pre class="example">     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 of

union type is equivalent to storing in a member of the union:



<pre class="example">     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="example">     void hack (union foo);

     /* <small class="dots">...</small> */

     hack ((union foo) x);

     </pre>



   </body></html>
⌨️ 快捷键说明

复制代码 Ctrl + C
搜索代码 Ctrl + F
全屏模式 F11
切换主题 Ctrl + Shift + D
显示快捷键 ?
增大字号 Ctrl + =
减小字号 Ctrl + -