| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|---|
| 2 | <html>
|
|---|
| 3 | <!-- Copyright (C) 2022 Richard Stallman and Free Software Foundation, Inc.
|
|---|
| 4 |
|
|---|
| 5 | (The work of Trevis Rothwell and Nelson Beebe has been assigned or
|
|---|
| 6 | licensed to the FSF.)
|
|---|
| 7 |
|
|---|
| 8 | Permission is granted to copy, distribute and/or modify this document
|
|---|
| 9 | under the terms of the GNU Free Documentation License, Version 1.3 or
|
|---|
| 10 | any later version published by the Free Software Foundation; with the
|
|---|
| 11 | Invariant Sections being "GNU General Public License," with the
|
|---|
| 12 | Front-Cover Texts being "A GNU Manual," and with the Back-Cover
|
|---|
| 13 | Texts as in (a) below. A copy of the license is included in the
|
|---|
| 14 | section entitled "GNU Free Documentation License."
|
|---|
| 15 |
|
|---|
| 16 | (a) The FSF's Back-Cover Text is: "You have the freedom to copy and
|
|---|
| 17 | modify this GNU manual. Buying copies from the FSF supports it in
|
|---|
| 18 | developing GNU and promoting software freedom." -->
|
|---|
| 19 | <!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|---|
| 20 | <head>
|
|---|
| 21 | <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|---|
| 22 | <title>Structure Constructors (GNU C Language Manual)</title>
|
|---|
| 23 |
|
|---|
| 24 | <meta name="description" content="Structure Constructors (GNU C Language Manual)">
|
|---|
| 25 | <meta name="keywords" content="Structure Constructors (GNU C Language Manual)">
|
|---|
| 26 | <meta name="resource-type" content="document">
|
|---|
| 27 | <meta name="distribution" content="global">
|
|---|
| 28 | <meta name="Generator" content="makeinfo">
|
|---|
| 29 | <link href="index.html" rel="start" title="Top">
|
|---|
| 30 | <link href="Symbol-Index.html" rel="index" title="Symbol Index">
|
|---|
| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|---|
| 32 | <link href="Structures.html" rel="up" title="Structures">
|
|---|
| 33 | <link href="Unnamed-Types-as-Fields.html" rel="next" title="Unnamed Types as Fields">
|
|---|
| 34 | <link href="Cast-to-Union.html" rel="prev" title="Cast to Union">
|
|---|
| 35 | <style type="text/css">
|
|---|
| 36 | <!--
|
|---|
| 37 | a.summary-letter {text-decoration: none}
|
|---|
| 38 | blockquote.indentedblock {margin-right: 0em}
|
|---|
| 39 | div.display {margin-left: 3.2em}
|
|---|
| 40 | div.example {margin-left: 3.2em}
|
|---|
| 41 | div.lisp {margin-left: 3.2em}
|
|---|
| 42 | kbd {font-style: oblique}
|
|---|
| 43 | pre.display {font-family: inherit}
|
|---|
| 44 | pre.format {font-family: inherit}
|
|---|
| 45 | pre.menu-comment {font-family: serif}
|
|---|
| 46 | pre.menu-preformatted {font-family: serif}
|
|---|
| 47 | span.nolinebreak {white-space: nowrap}
|
|---|
| 48 | span.roman {font-family: initial; font-weight: normal}
|
|---|
| 49 | span.sansserif {font-family: sans-serif; font-weight: normal}
|
|---|
| 50 | ul.no-bullet {list-style: none}
|
|---|
| 51 | -->
|
|---|
| 52 | </style>
|
|---|
| 53 |
|
|---|
| 54 |
|
|---|
| 55 | </head>
|
|---|
| 56 |
|
|---|
| 57 | <body lang="en">
|
|---|
| 58 | <span id="Structure-Constructors"></span><div class="header">
|
|---|
| 59 | <p>
|
|---|
| 60 | Next: <a href="Unnamed-Types-as-Fields.html" accesskey="n" rel="next">Unnamed Types as Fields</a>, Previous: <a href="Cast-to-Union.html" accesskey="p" rel="prev">Cast to Union</a>, Up: <a href="Structures.html" accesskey="u" rel="up">Structures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
|
|---|
| 61 | </div>
|
|---|
| 62 | <hr>
|
|---|
| 63 | <span id="Structure-Constructors-1"></span><h3 class="section">15.16 Structure Constructors</h3>
|
|---|
| 64 | <span id="index-structure-constructors"></span>
|
|---|
| 65 | <span id="index-constructors_002c-structure"></span>
|
|---|
| 66 |
|
|---|
| 67 | <p>You can construct a structure value by writing its type in
|
|---|
| 68 | parentheses, followed by an initializer that would be valid in a
|
|---|
| 69 | declaration for that type. For instance, given this declaration,
|
|---|
| 70 | </p>
|
|---|
| 71 | <div class="example">
|
|---|
| 72 | <pre class="example">struct foo {int a; char b[2];} structure;
|
|---|
| 73 | </pre></div>
|
|---|
| 74 |
|
|---|
| 75 | <p>you can create a <code>struct foo</code> value as follows:
|
|---|
| 76 | </p>
|
|---|
| 77 | <div class="example">
|
|---|
| 78 | <pre class="example">((struct foo) {x + y, 'a', 0})
|
|---|
| 79 | </pre></div>
|
|---|
| 80 |
|
|---|
| 81 | <p>This specifies <code>x + y</code> for field <code>a</code>,
|
|---|
| 82 | the character ‘<samp>a</samp>’ for field <code>b</code>’s element 0,
|
|---|
| 83 | and the null character for field <code>b</code>’s element 1.
|
|---|
| 84 | </p>
|
|---|
| 85 | <p>The parentheses around that constructor are to necessary, but we
|
|---|
| 86 | recommend writing them to make the nesting of the containing
|
|---|
| 87 | expression clearer.
|
|---|
| 88 | </p>
|
|---|
| 89 | <p>You can also show the nesting of the two by writing it like
|
|---|
| 90 | this:
|
|---|
| 91 | </p>
|
|---|
| 92 | <div class="example">
|
|---|
| 93 | <pre class="example">((struct foo) {x + y, {'a', 0} })
|
|---|
| 94 | </pre></div>
|
|---|
| 95 |
|
|---|
| 96 | <p>Each of those is equivalent to writing the following statement
|
|---|
| 97 | expression (see <a href="Statement-Exprs.html">Statement Exprs</a>):
|
|---|
| 98 | </p>
|
|---|
| 99 | <div class="example">
|
|---|
| 100 | <pre class="example">({
|
|---|
| 101 | struct foo temp = {x + y, 'a', 0};
|
|---|
| 102 | temp;
|
|---|
| 103 | })
|
|---|
| 104 | </pre></div>
|
|---|
| 105 |
|
|---|
| 106 | <p>You can also create a union value this way, but it is not especially
|
|---|
| 107 | useful since that is equivalent to doing a cast:
|
|---|
| 108 | </p>
|
|---|
| 109 | <div class="example">
|
|---|
| 110 | <pre class="example"> ((union whosis) {<var>value</var>})
|
|---|
| 111 | <span class="roman">is equivalent to</span>
|
|---|
| 112 | ((union whosis) (<var>value</var>))
|
|---|
| 113 | </pre></div>
|
|---|
| 114 |
|
|---|
| 115 |
|
|---|
| 116 |
|
|---|
| 117 |
|
|---|
| 118 | </body>
|
|---|
| 119 | </html>
|
|---|
