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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) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>shmget</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="shmget"></a> <a name="tag_03_678"></a><!-- shmget --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_678_01"></a>NAME</h4><blockquote>shmget - get an XSI shared memory segment</blockquote><h4><a name="tag_03_678_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/shm.h.html">sys/shm.h</a>><br><br> int shmget(key_t</tt> <i>key</i><tt>, size_t</tt> <i>size</i><tt>, int</tt> <i>shmflg</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_678_03"></a>DESCRIPTION</h4><blockquote><p>The <i>shmget</i>() function operates on XSI shared memory (see the Base Definitions volume of IEEE Std 1003.1-2001,<a href="../basedefs/xbd_chap03.html#tag_03_340">Section 3.340, Shared Memory Object</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>shmget</i>() function shall return the shared memory identifier associated with <i>key</i>.</p><p>A shared memory identifier, associated data structure, and shared memory segment of at least <i>size</i> bytes (see <a href="../basedefs/sys/shm.h.html"><i><sys/shm.h></i></a>) are created for <i>key</i> if one of the following is true:</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 shared memory identifier associated with it and (<i>shmflg</i> &IPC_CREAT)is non-zero.</p></li></ul><p>Upon creation, the data structure associated with the new shared memory identifier shall be initialized as follows:</p><ul><li><p>The values of <i>shm_perm.cuid</i>, <i>shm_perm.uid</i>, <i>shm_perm.cgid</i>, and <i>shm_perm.gid</i> are set equal to theeffective user ID and effective group ID, respectively, of the calling process.</p></li><li><p>The low-order nine bits of <i>shm_perm.mode</i> are set equal to the low-order nine bits of <i>shmflg</i>.</p></li><li><p>The value of <i>shm_segsz</i> is set equal to the value of <i>size</i>.</p></li><li><p>The values of <i>shm_lpid</i>, <i>shm_nattch</i>, <i>shm_atime</i>, and <i>shm_dtime</i> are set equal to 0.</p></li><li><p>The value of <i>shm_ctime</i> is set equal to the current time.</p></li></ul><p>When the shared memory segment is created, it shall be initialized with all zero values.</p></blockquote><h4><a name="tag_03_678_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>shmget</i>() shall return a non-negative integer, namely a shared memory identifier; otherwise,it shall return -1 and set <i>errno</i> to indicate the error.</p></blockquote><h4><a name="tag_03_678_05"></a>ERRORS</h4><blockquote><p>The <i>shmget</i>() function shall fail if:</p><dl compact><dt>[EACCES</dt><dd>A shared memory identifier exists for <i>key</i> but operation permission as specified by the low-order nine bits of<i>shmflg</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 shared memory identifier exists for the argument <i>key</i> but (<i>shmflg</i> &IPC_CREAT) &&(<i>shmflg</i>&IPC_EXCL) is non-zero.</dd><dt>[EINVAL]</dt><dd>A shared memory segment is to be created and the value of size is less than the system-imposed minimum or greater than thesystem-imposed maximum.</dd><dt>[EINVAL]</dt><dd>No shared memory segment is to be created and a shared memory segment exists for <i>key</i> but the size of the segmentassociated with it is less than <i>size</i> and <i>size</i> is not 0.</dd><dt>[ENOENT]</dt><dd>A shared memory identifier does not exist for the argument <i>key</i> and (<i>shmflg</i> &IPC_CREAT) is 0.</dd><dt>[ENOMEM]</dt><dd>A shared memory identifier and associated shared memory segment shall be created, but the amount of available physical memoryis not sufficient to fill the request.</dd><dt>[ENOSPC]</dt><dd>A shared memory identifier is to be created, but the system-imposed limit on the maximum number of allowed shared memoryidentifiers 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_678_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_678_07"></a>APPLICATION USAGE</h4><blockquote><p>The POSIX Realtime Extension defines alternative interfaces for interprocess communication. Application developers who need touse 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_678_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_678_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_678_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="shmat.html"><i>shmat</i>()</a>, <a href="shmctl.html"><i>shmctl</i>()</a>, <a href="shmdt.html"><i>shmdt</i>()</a>, <a href="shm_open.html"><i>shm_open</i>()</a>, <ahref="shm_unlink.html"><i>shm_unlink</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/sys/shm.h.html"><i><sys/shm.h></i></a></p></blockquote><h4><a name="tag_03_678_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_678_12"></a>Issue 5</h4><blockquote><p>Moved from SHARED MEMORY to BASE.</p><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 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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