208 lines
6.9 KiB
HTML
208 lines
6.9 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>ftok</title>
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<basefont size="3"> <a name="ftok"></a> <a name="tag_03_198"></a><!-- ftok -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_198_01"></a>NAME</h4>
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<blockquote>ftok - generate an IPC key</blockquote>
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<h4><a name="tag_03_198_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/sys/ipc.h.html">sys/ipc.h</a>><br>
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<br>
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key_t ftok(const char *</tt><i>path</i><tt>, int</tt> <i>id</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_198_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>ftok</i>() function shall return a key based on <i>path</i> and <i>id</i> that is usable in subsequent calls to <a href=
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"../functions/msgget.html"><i>msgget</i>()</a>, <a href="../functions/semget.html"><i>semget</i>()</a>, and <a href=
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"../functions/shmget.html"><i>shmget</i>()</a>. The application shall ensure that the <i>path</i> argument is the pathname of an
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existing file that the process is able to <a href="../functions/stat.html"><i>stat</i>()</a>.</p>
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<p>The <i>ftok</i>() function shall return the same key value for all paths that name the same file, when called with the same
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<i>id</i> value, and return different key values when called with different <i>id</i> values or with paths that name different
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files existing on the same file system at the same time. It is unspecified whether <i>ftok</i>() shall return the same key value
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when called again after the file named by <i>path</i> is removed and recreated with the same name.</p>
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<p>Only the low-order 8-bits of <i>id</i> are significant. The behavior of <i>ftok</i>() is unspecified if these bits are 0.</p>
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</blockquote>
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<h4><a name="tag_03_198_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>ftok</i>() shall return a key. Otherwise, <i>ftok</i>() shall return (<b>key_t</b>)-1 and set
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<i>errno</i> to indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_198_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>ftok</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EACCES]</dt>
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<dd>Search permission is denied for a component of the path prefix.</dd>
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<dt>[ELOOP]</dt>
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<dd>A loop exists in symbolic links encountered during resolution of the <i>path</i> argument.</dd>
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<dt>[ENAMETOOLONG]</dt>
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<dd>
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The length of the <i>path</i> argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.</dd>
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<dt>[ENOENT]</dt>
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<dd>A component of <i>path</i> does not name an existing file or <i>path</i> is an empty string.</dd>
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<dt>[ENOTDIR]</dt>
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<dd>A component of the path prefix is not a directory.</dd>
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</dl>
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<p>The <i>ftok</i>() function may fail if:</p>
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<dl compact>
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<dt>[ELOOP]</dt>
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<dd>More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the <i>path</i> argument.</dd>
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<dt>[ENAMETOOLONG]</dt>
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<dd>
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Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_198_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_198_06_01"></a>Getting an IPC Key</h5>
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<p>The following example gets a unique key that can be used by the IPC functions <a href=
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"../functions/semget.html"><i>semget</i>()</a>, <a href="../functions/msgget.html"><i>msgget</i>()</a>, and <a href=
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"../functions/shmget.html"><i>shmget</i>()</a>. The key returned by <i>ftok</i>() for this example is based on the ID value
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<i>S</i> and the pathname <b>/tmp</b>.</p>
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<pre>
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<tt>#include <sys/ipc.h>
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...
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key_t key;
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char *path = "/tmp";
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int id = 'S';
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<br>
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key = ftok(path, id);
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</tt>
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</pre>
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<h5><a name="tag_03_198_06_02"></a>Saving an IPC Key</h5>
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<p>The following example gets a unique key based on the pathname <b>/tmp</b> and the ID value <i>a</i>. It also assigns the value
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of the resulting key to the <i>semkey</i> variable so that it will be available to a later call to <a href=
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"../functions/semget.html"><i>semget</i>()</a>, <a href="../functions/msgget.html"><i>msgget</i>()</a>, or <a href=
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"../functions/shmget.html"><i>shmget</i>()</a>.</p>
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<pre>
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<tt>#include <sys/ipc.h>
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...
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key_t semkey;
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<br>
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if ((semkey = ftok("/tmp", 'a')) == (key_t) -1) {
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perror("IPC error: ftok"); exit(1);
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}
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_198_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>For maximum portability, <i>id</i> should be a single-byte character.</p>
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</blockquote>
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<h4><a name="tag_03_198_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_198_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_198_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="msgget.html"><i>msgget</i>()</a> , <a href="semget.html"><i>semget</i>()</a> , <a href=
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"shmget.html"><i>shmget</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/ipc.h.html"><i><sys/ipc.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_198_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4, Version 2.</p>
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</blockquote>
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<h4><a name="tag_03_198_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE.</p>
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</blockquote>
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<h4><a name="tag_03_198_13"></a>Issue 6</h4>
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<blockquote>
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<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
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<p>The wording of the mandatory [ELOOP] error condition is updated, and a second optional [ELOOP] error condition is added.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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