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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="Unnamed%20Fields">Unnamed Fields</a>,Next: <a rel="next" accesskey="n" href="Thread-Local.html#Thread-Local">Thread-Local</a>,Previous: <a rel="previous" accesskey="p" href="Pragmas.html#Pragmas">Pragmas</a>,Up: <a rel="up" accesskey="u" href="C-Extensions.html#C%20Extensions">C Extensions</a><hr><br></div><h3 class="section">Unnamed struct/union fields within structs/unions.</h3><p>For compatibility with other compilers, GCC allows you to definea structure or union that contains, as fields, structures and unionswithout names. For example:<pre class="smallexample"> struct { int a; union { int b; float c; }; int d; } foo; </pre> <p>In this example, the user would be able to access members of the unnamedunion with code like <code>foo.b</code>. Note that only unnamed structs andunions are allowed, you may not have, for example, an unnamed<code>int</code>. <p>You must never create such structures that cause ambiguous field definitions. For example, this structure:<pre class="smallexample"> struct { int a; struct { int a; }; } foo; </pre> <p>It is ambiguous which <code>a</code> is being referred to with <code>foo.a</code>. Such constructs are not supported and must be avoided. In the future,such constructs may be detected and treated as compilation errors. </body></html>⌨️ 快捷键说明
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