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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>msgget</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="msgget"></a> <a name="tag_03_394"></a><!-- msgget --> <!--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_394_01"></a>NAME</h4><blockquote>msgget - get the XSI message queue identifier</blockquote><h4><a name="tag_03_394_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/sys/msg.h.html">sys/msg.h</a>><br><br> int msgget(key_t</tt> <i>key</i><tt>, int</tt> <i>msgflg</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_394_03"></a>DESCRIPTION</h4><blockquote><p>The <i>msgget</i>() function operates on XSI message queues (see the Base Definitions volume of IEEE Std 1003.1-2001,<a href="../basedefs/xbd_chap03.html#tag_03_224">Section 3.224, Message Queue</a>). It is unspecified whether this functioninteroperates with the realtime interprocess communication facilities defined in <a href="xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> .</p><p>The <i>msgget</i>() function shall return the message queue identifier associated with the argument <i>key</i>.</p><p>A message queue identifier, associated message queue, and data structure (see <a href="../basedefs/sys/msg.h.html"><i><sys/msg.h></i></a>), shall be created for the argument <i>key</i> if one of the following istrue:</p><ul><li><p>The argument <i>key</i> is equal to IPC_PRIVATE.</p></li><li><p>The argument <i>key</i> does not already have a message queue identifier associated with it, and (<i>msgflg</i> & IPC_CREAT)is non-zero.</p></li></ul><p>Upon creation, the data structure associated with the new message queue identifier shall be initialized as follows:</p><ul><li><p><b>msg_perm.cuid</b>, <b>msg_perm.uid</b>, <b>msg_perm.cgid</b>, and <b>msg_perm.gid</b> shall be set equal to the effectiveuser ID and effective group ID, respectively, of the calling process.</p></li><li><p>The low-order 9 bits of <b>msg_perm.mode</b> shall be set equal to the low-order 9 bits of <i>msgflg</i>.</p></li><li><p><b>msg_qnum</b>, <b>msg_lspid</b>, <b>msg_lrpid</b>, <b>msg_stime</b>, and <b>msg_rtime</b> shall be set equal to 0.</p></li><li><p><b>msg_ctime</b> shall be set equal to the current time.</p></li><li><p><b>msg_qbytes</b> shall be set equal to the system limit.</p></li></ul></blockquote><h4><a name="tag_03_394_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>msgget</i>() shall return a non-negative integer, namely a message queue identifier. Otherwise,it shall return -1 and set <i>errno</i> to indicate the error.</p></blockquote><h4><a name="tag_03_394_05"></a>ERRORS</h4><blockquote><p>The <i>msgget</i>() function shall fail if:</p><dl compact><dt>[EACCES]</dt><dd>A message queue identifier exists for the argument <i>key</i>, but operation permission as specified by the low-order 9 bits of<i>msgflg</i> would not be granted; see <a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> .</dd><dt>[EEXIST]</dt><dd>A message queue identifier exists for the argument <i>key</i> but ((<i>msgflg</i> & IPC_CREAT) && (<i>msgflg</i>& IPC_EXCL)) is non-zero.</dd><dt>[ENOENT]</dt><dd>A message queue identifier does not exist for the argument <i>key</i> and (<i>msgflg</i> & IPC_CREAT) is 0.</dd><dt>[ENOSPC]</dt><dd>A message queue identifier is to be created but the system-imposed limit on the maximum number of allowed message queueidentifiers system-wide would be exceeded.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_394_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_394_07"></a>APPLICATION USAGE</h4><blockquote><p>The POSIX Realtime Extension defines alternative interfaces for interprocess communication (IPC). Application developers whoneed to use IPC should design their applications so that modules using the IPC routines described in <a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> can be easily modified to use the alternativeinterfaces.</p></blockquote><h4><a name="tag_03_394_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_394_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_394_10"></a>SEE ALSO</h4><blockquote><p><a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> , <a href="xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> , <a href="mq_close.html"><i>mq_close</i>()</a> , <a href="mq_getattr.html"><i>mq_getattr</i>()</a> , <a href="mq_notify.html"><i>mq_notify</i>()</a> , <a href="mq_open.html"><i>mq_open</i>()</a> , <a href="mq_receive.html"><i>mq_receive</i>()</a> , <a href="mq_send.html"><i>mq_send</i>()</a> , <a href="mq_setattr.html"><i>mq_setattr</i>()</a> , <a href="mq_unlink.html"><i>mq_unlink</i>()</a> , <a href="msgctl.html"><i>msgctl</i>()</a> , <a href="msgrcv.html"><i>msgrcv</i>()</a> ,<a href="msgsnd.html"><i>msgsnd</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/sys/msg.h.html"><i><sys/msg.h></i></a></p></blockquote><h4><a name="tag_03_394_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2. Derived from Issue 2 of the SVID.</p></blockquote><h4><a name="tag_03_394_12"></a>Issue 5</h4><blockquote><p>The note about use of POSIX Realtime Extension IPC routines has been moved from FUTURE DIRECTIONS to a new APPLICATION USAGEsection.</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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