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diff --git a/share/doc/gcc/Cast-to-Union.html b/share/doc/gcc/Cast-to-Union.html new file mode 100644 index 0000000..3639433 --- /dev/null +++ b/share/doc/gcc/Cast-to-Union.html @@ -0,0 +1,148 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). 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Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): Cast to Union</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Cast to Union"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Cast to Union"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions"> +<link href="Mixed-Labels-and-Declarations.html#Mixed-Labels-and-Declarations" rel="next" title="Mixed Labels and Declarations"> +<link href="Case-Ranges.html#Case-Ranges" rel="previous" title="Case Ranges"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Cast-to-Union"></a> +<div class="header"> +<p> +Next: <a href="Mixed-Labels-and-Declarations.html#Mixed-Labels-and-Declarations" accesskey="n" rel="next">Mixed Labels and Declarations</a>, Previous: <a href="Case-Ranges.html#Case-Ranges" accesskey="p" rel="previous">Case Ranges</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Cast-to-a-Union-Type"></a> +<h3 class="section">6.31 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 a union type is a C extension not available in C++. It looks +just like ordinary casts with the constraint that the type specified is +a union type. You can specify the type either with the <code>union</code> +keyword or with a <code>typedef</code> name that refers to a union. The result +of a cast to a union is a temporary rvalue of the union type with a member +whose type matches that of the operand initialized to the value of +the operand. The effect of a cast to a union is similar to a compound +literal except that it yields an rvalue like standard casts do. +See <a href="Compound-Literals.html#Compound-Literals">Compound Literals</a>. +</p> +<p>Expressions that may be cast to the union type are those whose type matches +at least one 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; +union foo z; +</pre></div> + +<p>both <code>x</code> and <code>y</code> can be cast to type <code>union foo</code> and +the following assignments +</p><div class="smallexample"> +<pre class="smallexample"> z = (union foo) x; + z = (union foo) y; +</pre></div> +<p>are shorthand equivalents of these +</p><div class="smallexample"> +<pre class="smallexample"> z = (union foo) { .i = x }; + z = (union foo) { .d = y }; +</pre></div> + +<p>However, <code>(union foo) FLT_MAX;</code> is not a valid cast because the union +has no member of type <code>float</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 with +the same type +</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> + +<hr> +<div class="header"> +<p> +Next: <a href="Mixed-Labels-and-Declarations.html#Mixed-Labels-and-Declarations" accesskey="n" rel="next">Mixed Labels and Declarations</a>, Previous: <a href="Case-Ranges.html#Case-Ranges" accesskey="p" rel="previous">Case Ranges</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |