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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>msgget</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_007_808"> </a>NAME</h4><blockquote>msgget - get the message queue identifier</blockquote><h4><a name = "tag_000_007_809"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="sysmsg.h.html">sys/msg.h</a>>int msgget(key_t <i>key</i>, int <i>msgflg</i>);</code></pre></blockquote><h4><a name = "tag_000_007_810"> </a>DESCRIPTION</h4><blockquote>The<i>msgget()</i>function returns the message queue identifier associated with the argument<i>key</i>.<p>A message queue identifier, associated message queue and data structure,see<i><a href="sysmsg.h.html"><sys/msg.h></a></i>,are created for the argument<i>key</i>if one of the following is true:<ul><p><li>The argument<i>key</i>is equal to IPC_PRIVATE.<p><li>The argument<i>key</i>does not already have a message queue identifierassociated with it, and (<i>msgflg</i> & IPC_CREAT) is non-zero.<p></ul><p>Upon creation, the data structure associated withthe new message queue identifier is initialised as follows:<ul><p><li><b>msg_perm.cuid</b>,<b>msg_perm.uid</b>,<b>msg_perm.cgid</b>and<b>msg_perm.gid</b>are set equal to the effective user IDand effective group ID, respectively, of the calling process.<p><li>The low-order 9 bits of<b>msg_perm.mode</b>are set equal to the low-order 9 bits of<i>msgflg</i>.<p><li><b>msg_qnum</b>,<b>msg_lspid</b>,<b>msg_lrpid</b>,<b>msg_stime</b>and<b>msg_rtime</b>are set equal to 0.<p><li><b>msg_ctime</b>is set equal to the current time.<p><li><b>msg_qbytes</b>is set equal to the system limit.<p></ul></blockquote><h4><a name = "tag_000_007_811"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>msgget()</i>returns a non-negative integer,namely a message queue identifier. Otherwise, it returns -1 and<i>errno</i>is set to indicate the error.</blockquote><h4><a name = "tag_000_007_812"> </a>ERRORS</h4><blockquote>The<i>msgget()</i>function will fail if:<dl compact><dt>[EACCES]<dd>A message queue identifier exists for the argument<i>key</i>,but operation permissionas specified by the low-order 9 bits of<i>msgflg</i>would not be granted, see<a href="ipc.html">IPC</a>.<dt>[EEXIST]<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.<dt>[ENOENT]<dd>A message queue identifier does not exist for the argument<i>key</i>and (<i>msgflg</i> & IPC_CREAT) is 0.<dt>[ENOSPC]<dd>A message queue identifier is to be created but thesystem-imposed limit on the maximum number of allowedmessage queue identifiers system-wide would be exceeded.</dl></blockquote><h4><a name = "tag_000_007_813"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_814"> </a>APPLICATION USAGE</h4><blockquote>The POSIX Realtime Extension defines alternative interfaces for interprocess communication.Application developers who need to use IPC should design theirapplications so that modules using the IPC routines described in<a href="ipc.html">IPC</a>can be easily modified to use the alternative interfaces.</blockquote><h4><a name = "tag_000_007_815"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_816"> </a>SEE ALSO</h4><blockquote><i><a href="mq_close.html">mq_close()</a></i>,<i><a href="mq_getattr.html">mq_getattr()</a></i>,<i><a href="mq_notify.html">mq_notify()</a></i>,<i><a href="mq_open.html">mq_open()</a></i>,<i><a href="mq_receive.html">mq_receive()</a></i>,<i><a href="mq_send.html">mq_send()</a></i>,<i><a href="mq_setattr.html">mq_setattr()</a></i>,<i><a href="mq_unlink.html">mq_unlink()</a></i>,<i><a href="msgctl.html">msgctl()</a></i>,<i><a href="msgrcv.html">msgrcv()</a></i>,<i><a href="msgsnd.html">msgsnd()</a></i>,<i><a href="sysmsg.h.html"><sys/msg.h></a></i>,<a href="ipc.html">IPC</a>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 2 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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