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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>sockatmark</title></head><body bgcolor="white"><basefont size="3"> <a name="sockatmark"></a> <a name="tag_03_707"></a><!-- sockatmark --> <!--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_707_01"></a>NAME</h4><blockquote>sockatmark - determine whether a socket is at the out-of-band mark</blockquote><h4><a name="tag_03_707_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/sys/socket.h.html">sys/socket.h</a>><br><br> int sockatmark(int</tt> <i>s</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_707_03"></a>DESCRIPTION</h4><blockquote><p>The <i>sockatmark</i>() function shall determine whether the socket specified by the descriptor <i>s</i> is at the out-of-banddata mark (see the System Interfaces volume of IEEE Std 1003.1-2001, <a href="../functions/xsh_chap02_10.html#tag_02_10_12">Section 2.10.12, Socket Out-of-Band State</a>). If the protocol for the socketsupports out-of-band data by marking the stream with an out-of-band data mark, the <i>sockatmark</i>() function shall return 1 whenall data preceding the mark has been read and the out-of-band data mark is the first element in the receive queue. The<i>sockatmark</i>() function shall not remove the mark from the stream.</p></blockquote><h4><a name="tag_03_707_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, the <i>sockatmark</i>() function shall return a value indicating whether the socket is at anout-of-band data mark. If the protocol has marked the data stream and all data preceding the mark has been read, the return valueshall be 1; if there is no mark, or if data precedes the mark in the receive queue, the <i>sockatmark</i>() function shall return0. Otherwise, it shall return a value of -1 and set <i>errno</i> to indicate the error.</p></blockquote><h4><a name="tag_03_707_05"></a>ERRORS</h4><blockquote><p>The <i>sockatmark</i>() function shall fail if:</p><dl compact><dt>[EBADF]</dt><dd>The <i>s</i> argument is not a valid file descriptor.</dd><dt>[ENOTTY]</dt><dd>The <i>s</i> argument does not specify a descriptor for a socket.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_707_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_707_07"></a>APPLICATION USAGE</h4><blockquote><p>The use of this function between receive operations allows an application to determine which received data precedes theout-of-band data and which follows the out-of-band data.</p><p>There is an inherent race condition in the use of this function. On an empty receive queue, the current read of the locationmight well be at the "mark", but the system has no way of knowing that the next data segment that will arrive from the networkwill carry the mark, and <i>sockatmark</i>() will return false, and the next read operation will silently consume the mark.</p><p>Hence, this function can only be used reliably when the application already knows that the out-of-band data has been seen by thesystem or that it is known that there is data waiting to be read at the socket (via SIGURG or <a href="../functions/select.html"><i>select</i>()</a>). See <a href="xsh_chap02_10.html#tag_02_10_11"><i>Socket Receive Queue</i></a> , <ahref="xsh_chap02_10.html#tag_02_10_12"><i>Socket Out-of-Band Data State</i></a> , <a href="xsh_chap02_10.html#tag_02_10_14"><i>Signals</i></a> , and <a href="../functions/pselect.html"><i>pselect</i>()</a> fordetails.</p></blockquote><h4><a name="tag_03_707_08"></a>RATIONALE</h4><blockquote><p>The <i>sockatmark</i>() function replaces the historical SIOCATMARK command to <a href="../functions/ioctl.html"><i>ioctl</i>()</a> which implemented the same functionality on many implementations. Using a wrapperfunction follows the adopted conventions to avoid specifying commands to the <a href="../functions/ioctl.html"><i>ioctl</i>()</a>function, other than those now included to support XSI STREAMS. The <i>sockatmark</i>() function could be implemented asfollows:</p><pre><tt>#include <sys/ioctl.h><br>int sockatmark(int s){ int val; if (ioctl(s,SIOCATMARK,&val)==-1) return(-1); return(val);}</tt></pre><p>The use of [ENOTTY] to indicate an incorrect descriptor type matches the historical behavior of SIOCATMARK.</p></blockquote><h4><a name="tag_03_707_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_707_10"></a>SEE ALSO</h4><blockquote><p><a href="pselect.html"><i>pselect</i>()</a> , <a href="recv.html"><i>recv</i>()</a> , <a href="recvmsg.html"><i>recvmsg</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/sys/socket.h.html"><i><sys/socket.h></i></a></p></blockquote><h4><a name="tag_03_707_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 6. Derived from IEEE Std 1003.1g-2000.</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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