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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>errno</title></head><body bgcolor="white"><basefont size="3"> <a name="errno"></a> <a name="tag_03_129"></a><!-- errno --> <!--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_03_129_01"></a>NAME</h4><blockquote>errno - error return value</blockquote><h4><a name="tag_03_129_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <errno.h></tt></code></p></blockquote><h4><a name="tag_03_129_03"></a>DESCRIPTION</h4><blockquote><p>The lvalue <i>errno</i> is used by many functions to return error values.</p><p>Many functions provide an error number in <i>errno</i>, which has type <b>int</b> and is defined in <a href="../basedefs/errno.h.html"><i><errno.h></i></a>. The value of <i>errno</i> shall be defined only after a call to a functionfor which it is explicitly stated to be set and until it is changed by the next function call or if the application assigns it avalue. The value of <i>errno</i> should only be examined when it is indicated to be valid by a function's return value.Applications shall obtain the definition of <i>errno</i> by the inclusion of <a href="../basedefs/errno.h.html"><i><errno.h></i></a>. No function in this volume of IEEE Std 1003.1-2001 shall set<i>errno</i> to 0.</p><p>It is unspecified whether <i>errno</i> is a macro or an identifier declared with external linkage. If a macro definition issuppressed in order to access an actual object, or a program defines an identifier with the name <i>errno</i>, the behavior isundefined.</p><p>The symbolic values stored in <i>errno</i> are documented in the ERRORS sections on all relevant pages.</p></blockquote><h4><a name="tag_03_129_04"></a>RETURN VALUE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_129_05"></a>ERRORS</h4><blockquote><p>None.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_129_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_129_07"></a>APPLICATION USAGE</h4><blockquote><p>Previously both POSIX and X/Open documents were more restrictive than the ISO C standard in that they required <i>errno</i>to be defined as an external variable, whereas the ISO C standard required only that <i>errno</i> be defined as a modifiablelvalue with type <b>int</b>.</p><p>An application that needs to examine the value of <i>errno</i> to determine the error should set it to 0 before a function call,then inspect it before a subsequent function call.</p></blockquote><h4><a name="tag_03_129_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_129_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_129_10"></a>SEE ALSO</h4><blockquote><p><a href="xsh_chap02_03.html#tag_02_03"><i>Error Numbers</i></a> , the Base Definitions volume of IEEE Std 1003.1-2001,<a href="../basedefs/errno.h.html"><i><errno.h></i></a></p></blockquote><h4><a name="tag_03_129_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 1. Derived from Issue 1 of the SVID.</p></blockquote><h4><a name="tag_03_129_12"></a>Issue 5</h4><blockquote><p>The following sentence is deleted from the DESCRIPTION: "The value of <i>errno</i> is 0 at program start-up, but is never setto 0 by any XSI function". The DESCRIPTION also no longer states that conforming implementations may support the declaration:</p><pre><tt>extern int errno;</tt></pre></blockquote><h4><a name="tag_03_129_13"></a>Issue 6</h4><blockquote><p>Obsolescent text regarding defining <i>errno</i> as:</p><pre><tt>extern int errno</tt></pre><p>is removed.</p><p>Text regarding no function setting <i>errno</i> to zero to indicate an error is changed to no function shall set <i>errno</i> tozero. This is for alignment with the ISO/IEC 9899:1999 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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