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📁 自己收集的linux入门到学懂高级编程书集包括linux程序设计第三版
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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 &copy; 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:&nbsp;<a name="Alignment">Alignment</a>,Next:&nbsp;<a rel="next" accesskey="n" href="Inline.html#Inline">Inline</a>,Previous:&nbsp;<a rel="previous" accesskey="p" href="Type-Attributes.html#Type%20Attributes">Type Attributes</a>,Up:&nbsp;<a rel="up" accesskey="u" href="C-Extensions.html#C%20Extensions">C Extensions</a><hr><br></div><h3 class="section">Inquiring on Alignment of Types or Variables</h3><p>The keyword <code>__alignof__</code> allows you to inquire about how an objectis aligned, or the minimum alignment usually required by a type.  Itssyntax is just like <code>sizeof</code>.   <p>For example, if the target machine requires a <code>double</code> value to bealigned on an 8-byte boundary, then <code>__alignof__ (double)</code> is 8. This is true on many RISC machines.  On more traditional machinedesigns, <code>__alignof__ (double)</code> is 4 or even 2.   <p>Some machines never actually require alignment; they allow reference to anydata type even at an odd address.  For these machines, <code>__alignof__</code>reports the <em>recommended</em> alignment of a type.   <p>If the operand of <code>__alignof__</code> is an lvalue rather than a type,its value is the required alignment for its type, taking into accountany minimum alignment specified with GCC's <code>__attribute__</code>extension (see <a href="Variable-Attributes.html#Variable%20Attributes">Variable Attributes</a>).  For example, after thisdeclaration:<pre class="smallexample">     struct foo { int x; char y; } foo1;     </pre><p>the value of <code>__alignof__ (foo1.y)</code> is 1, even though its actualalignment is probably 2 or 4, the same as <code>__alignof__ (int)</code>.   <p>It is an error to ask for the alignment of an incomplete type.   </body></html>
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