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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title><stddef.h></title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="<stddef.h>"></a> <a name="tag_13_47"></a><!-- <stddef.h> --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_13_47_01"></a>NAME</h4><blockquote>stddef.h - standard type definitions</blockquote><h4><a name="tag_13_47_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><tt>#include <stddef.h></tt></p></blockquote><h4><a name="tag_13_47_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>The <i><stddef.h></i> header shall define the following macros:</p><dl compact><dt>NULL</dt><dd>Null pointer constant.</dd><dt>offsetof(<i>type</i>, <i>member-designator</i>)</dt><dd><br>Integer constant expression of type <b>size_t</b>, the value of which is the offset in bytes to the structure member(<i>member-designator</i>), from the beginning of its structure (<i>type</i>).</dd></dl><p>The <i><stddef.h></i> header shall define the following types:</p><dl compact><dt><b>ptrdiff_t</b></dt><dd>Signed integer type of the result of subtracting two pointers.</dd><dt><b>wchar_t</b></dt><dd>Integer type whose range of values can represent distinct wide-character codes for all members of the largest character setspecified among the locales supported by the compilation environment: the null character has the code value 0 and each member ofthe portable character set has a code value equal to its value when used as the lone character in an integer characterconstant.</dd><dt><b>size_t</b></dt><dd>Unsigned integer type of the result of the <i>sizeof</i> operator.</dd></dl><p>The implementation shall support one or more programming environments in which the widths of <b>ptrdiff_t</b>, <b>size_t</b>,and <b>wchar_t</b> are no greater than the width of type <b>long</b>. The names of these programming environments can be obtainedusing the <a href="../functions/confstr.html"><i>confstr</i>()</a> function or the <a href="../utilities/getconf.html"><i>getconf</i></a> utility.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_13_47_04"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_47_05"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_47_06"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_47_07"></a>SEE ALSO</h4><blockquote><p><a href="wchar.h.html"><i><wchar.h></i></a> , <a href="sys/types.h.html"><i><sys/types.h></i></a> , the SystemInterfaces volume of IEEE Std 1003.1-2001, <a href="../functions/confstr.html"><i>confstr</i>()</a>, the Shell andUtilities volume of IEEE Std 1003.1-2001, <a href="../utilities/getconf.html"><i>getconf</i></a></p></blockquote><h4><a name="tag_13_47_08"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4. Derived from the ANSI C standard.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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