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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>sigemptyset</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="sigemptyset"></a> <a name="tag_03_684"></a><!-- sigemptyset --> <!--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_684_01"></a>NAME</h4><blockquote>sigemptyset - initialize and empty a signal set</blockquote><h4><a name="tag_03_684_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/signal.h.html">signal.h</a>><br><br> int sigemptyset(sigset_t *</tt><i>set</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_684_03"></a>DESCRIPTION</h4><blockquote><p>The <i>sigemptyset</i>() function initializes the signal set pointed to by <i>set</i>, such that all signals defined inIEEE Std 1003.1-2001 are excluded.</p></blockquote><h4><a name="tag_03_684_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>sigemptyset</i>() shall return 0; otherwise, it shall return -1 and set <i>errno</i> to indicatethe error.</p></blockquote><h4><a name="tag_03_684_05"></a>ERRORS</h4><blockquote><p>No errors are defined.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_684_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_684_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_684_08"></a>RATIONALE</h4><blockquote><p>The implementation of the <i>sigemptyset</i>() (or <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a>) functioncould quite trivially clear (or set) all the bits in the signal set. Alternatively, it would be reasonable to initialize part ofthe structure, such as a version field, to permit binary-compatibility between releases where the size of the set varies. For suchreasons, either <i>sigemptyset</i>() or <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a> must be called prior to anyother use of the signal set, even if such use is read-only (for example, as an argument to <a href="../functions/sigpending.html"><i>sigpending</i>()</a>). This function is not intended for dynamic allocation.</p><p>The <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a> and <i>sigemptyset</i>() functions require that the resultingsignal set include (or exclude) all the signals defined in this volume of IEEE Std 1003.1-2001. Although it is outsidethe scope of this volume of IEEE Std 1003.1-2001 to place this requirement on signals that are implemented as extensions,it is recommended that implementation-defined signals also be affected by these functions. However, there may be a good reason fora particular signal not to be affected. For example, blocking or ignoring an implementation-defined signal may have undesirableside effects, whereas the default action for that signal is harmless. In such a case, it would be preferable for such a signal tobe excluded from the signal set returned by <a href="../functions/sigfillset.html"><i>sigfillset</i>()</a>.</p><p>In early proposals there was no distinction between invalid and unsupported signals (the names of optional signals that were notsupported by an implementation were not defined by that implementation). The [EINVAL] error was thus specified as a required errorfor invalid signals. With that distinction, it is not necessary to require implementations of these functions to determine whetheran optional signal is actually supported, as that could have a significant performance impact for little value. The error couldhave been required for invalid signals and optional for unsupported signals, but this seemed unnecessarily complex. Thus, the erroris optional in both cases.</p></blockquote><h4><a name="tag_03_684_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_684_10"></a>SEE ALSO</h4><blockquote><p><a href="xsh_chap02_04.html#tag_02_04"><i>Signal Concepts</i></a> , <a href="sigaction.html"><i>sigaction</i>()</a> , <a href="sigaddset.html"><i>sigaddset</i>()</a> , <a href="sigdelset.html"><i>sigdelset</i>()</a> , <a href="sigfillset.html"><i>sigfillset</i>()</a> , <a href="sigismember.html"><i>sigismember</i>()</a> , <a href="sigpending.html"><i>sigpending</i>()</a> , <a href="sigprocmask.html"><i>sigprocmask</i>()</a> , <a href="sigsuspend.html"><i>sigsuspend</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/signal.h.html"><i><signal.h></i></a></p></blockquote><h4><a name="tag_03_684_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 3. Included for alignment with the POSIX.1-1988 standard.</p></blockquote><h4><a name="tag_03_684_12"></a>Issue 6</h4><blockquote><p>The SYNOPSIS is marked CX since the presence of this function in the <a href="../basedefs/signal.h.html"><i><signal.h></i></a> header is an extension over the ISO 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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