418 lines
11 KiB
HTML
418 lines
11 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>dup2()--Duplicate Open File Descriptor to Another Descriptor</title>
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<!-- Begin Header Records ========================================== -->
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Change History: -->
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<!-- YYMMDD USERID Change description -->
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<!-- Unix2 SCRIPT J converted by B2H R4.1 (346) (CMS) by V2KEA304 -->
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<!-- at RCHVMW2 on 17 Feb 1999 at 11:05:09 -->
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<!-- 011022 JTROUS Changes from API Review 1, V5R2 -->
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<!-- 020313 JTROUS Changes for scan processing, V5R3, DCR 98680 -->
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<!-- 020618 EMIG Updates for NFS threadsafety, V5R3 -->
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<!-- 0206?? JET This file has undergone html cleanup -->
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<!-- 020718 MFENLON: updated for QFileSvr.400 threadsafety, V5R3 -->
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<!-- 050323 JTROUS: fix enums, no change flag, V5R4 -->
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<!-- 050817 JTROUS: add cross link to close API, v5r4 -->
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<!-- End Header Records -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!-- Java sync-link -->
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<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>dup2()--Duplicate Open File Descriptor to Another Descriptor</h2>
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<div class="box" style="width: 70%;">
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<br>
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Syntax<br>
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<pre>
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#include <unistd.h>
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int dup2(int <em>fildes</em>, int <em>fildes2</em>);
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</pre>
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Service Program Name: QP0LLIB1<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Conditional; see <a href="#usage_notes">Usage Notes</a>.<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>dup2()</strong> function returns a descriptor with the value
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<em>fildes2</em>. The descriptor refers to the same file as <em>fildes</em>,
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and it will close the file that <em>fildes2</em> was associated with.
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<img src="delta.gif" alt="Start of change">
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For more information on the processing which may occur when the file is
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closed, see <a href="close.htm">close()</a>--Close File or Socket Descriptor.
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<img src="deltaend.gif" alt="End of change">
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</p>
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<p>If the original file descriptor was opened in text mode, data conversion is
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also done on the duplicated file descriptor.</p>
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<p>The FD_CLOEXEC flag that is associated with the new file descriptor is
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cleared. Refer to <a href="fcntl.htm">fcntl()</a>--Perform File Control Command
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for additional information about the FD_CLOEXEC flag.</p>
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<p>The following conditions apply:</p>
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<ul>
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<li>If <em>fildes2</em> is less than zero or greater than or equal to OPEN_MAX,
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<strong>dup2()</strong> returns -<samp>1</samp> and sets the <em>errno</em>
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global variable to [EBADF].<br>
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</li>
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<li>If <em>fildes</em> is a valid descriptor and is equal to <em>fildes2</em>,
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<strong>dup2()</strong> returns <em>fildes2</em> without closing it.<br>
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</li>
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<li>If <em>fildes</em> is not a valid descriptor, <strong>dup2()</strong> fails
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and does not close <em>fildes2</em>.</li>
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</ul>
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<p>This function works with descriptors for any type of object.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong><em>fildes</em></strong></dt>
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<dd>(Input) A descriptor to be duplicated.<br>
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</dd>
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<dt><strong><em>fildes2</em></strong></dt>
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<dd>(Input) The descriptor to which the duplication is made.</dd>
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</dl>
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<br>
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<h3>Authorities</h3>
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<p>No authorization is required.</p>
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<br>
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<h3>Return Value</h3>
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<dl compact>
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<dt><em>value</em></dt>
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<dd><strong>dup2()</strong> was successful. The value of <em>fildes2</em> is
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returned.</dd>
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<dt><em>-1</em></dt>
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<dd><strong>dup2()</strong> was not successful. The <em>errno</em> global
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variable is set to indicate the error.</dd>
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</dl>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>dup2()</strong> is not successful, <em>errno</em> usually
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indicates one of the following errors. Under some conditions, <em>errno</em>
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could indicate an error other than those listed here.</p>
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<table cellpadding="5">
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<!-- cols="25 75" -->
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<tr>
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<th align="left" valign="bottom">Error condition</th>
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<th align="left" valign="bottom">Additional information</th>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#EACCES">EACCES</a>]</em></td>
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<td align="left" valign="top">
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<p>If you are accessing a remote file through the Network File System, update
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operations to file permissions at the server are not reflected at the client
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until updates to data that is stored locally by the Network File System take
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place. (Several options on the Add Mounted File System (ADDMFS) command
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determine the time between refresh operations of local data.) Access to a
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remote file may also fail due to different mappings of user IDs (UID) or group
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IDs (GID) on the local and remote systems.</p>
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#EBADF">EBADF</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#EBADFID">EBADFID</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#EIO">EIO</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#ENOTSAFE">ENOTSAFE</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#ENOTSUP">ENOTSUP</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#ESTALE">ESTALE</a>]</em></td>
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<td align="left" valign="top">
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<p>If you are accessing a remote file through the Network File System, the file
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may have been deleted at the server.</p>
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</td>
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</tr>
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<tr>
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<td align="left" valign="top">
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<em>[<a href="unix14.htm#EUNKNOWN">EUNKNOWN</a>]</em></td>
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<td align="left" valign="top">
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</td>
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</tr>
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</table>
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<br>
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<br>
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<h3>Error Messages</h3>
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<p>The following messages may be sent from this function:</p>
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<table width="100%" cellpadding="5">
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<!-- cols="15 85" -->
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<tr>
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<th align="left" valign="top">Message ID</th>
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<th align="left" valign="top">Error Message Text</th>
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</tr>
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<tr>
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<td width="15%" valign="top">CPE3418 E</td>
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<td width="85%" valign="top">Possible APAR condition or hardware failure.</td>
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</tr>
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<tr>
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<td valign="top">CPFA0D4 E</td>
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<td valign="top">File system error occurred. Error number &1.</td>
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</tr>
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<tr>
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<td valign="top">CPF3CF2 E</td>
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<td valign="top">Error(s) occurred during running of &1 API.</td>
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</tr>
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<tr>
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<td valign="top">CPF9872 E</td>
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<td valign="top">Program or service program &1 in library &2 ended.
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Reason code &3.</td>
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</tr>
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</table>
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<br>
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<h3><a name="usage_notes">Usage Notes</a></h3>
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<ol type="1">
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<li>If this function is called
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by a thread executing one of the scan-related exit programs (or any of its
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created threads), it will fail with error code [ENOTSUP]. See <a href=
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"ifsopenexit.htm">Integrated File System Scan on Open Exit Programs</a> and <a
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href="ifscloseexit.htm">Integrated File System Scan on Close Exit Programs</a>
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for more information. <br>
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<br>
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</li>
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<li>This function will fail with error code [ENOTSAFE] when all the following
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conditions are true:
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<ul>
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<li>Where multiple threads exist in the job.<br>
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</li>
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<li>The object on which this function is operating resides in a file system
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that is not threadsafe. Only the following file systems are threadsafe for this
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function:
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<ul>
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<li>"Root" (/)</li>
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<li>QOpenSys</li>
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<li>User-defined</li>
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<li>QNTC</li>
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<li>QSYS.LIB</li>
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<li>Independent ASP QSYS.LIB</li>
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<li>QOPT</li>
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<li>Network File System</li>
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<li>QFileSvr.400</li>
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</ul>
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</li>
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</ul>
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</li>
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</ol>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li>The <<strong>unistd.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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</li>
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<li><a href="close.htm">close()</a>--Close File or Socket Descriptor<br>
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</li>
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<li><a href="creat.htm">creat()</a>--Create or Rewrite File<br>
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</li>
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<li><a href="dup.htm">dup()</a>--Duplicate Open File Descriptor<br>
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</li>
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<li><a href="fcntl.htm">fcntl()</a>--Perform File Control Command<br>
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</li>
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<li><a href="open.htm">open()</a>--Open File</li>
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</ul>
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<br>
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<h3>Example</h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<p>The following example duplicates an open descriptor:</p>
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<pre>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <errno.h>
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void print_file_id(int file_descriptor) {
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struct stat info;
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if (fstat(file_descriptor, &info) != 0)
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fprintf(stderr, "stat() error for file_descriptor %d: %s\n",
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strerror(errno));
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else
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printf("The file id of file_descriptor %d is %d\n", file_descriptor,
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(int) info.st_ino);
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}
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main() {
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int file_descriptor, file_descriptor2;
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char fn[] = "original.file";
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char fn2[] = "dup2.file";
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/* create original file */
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if((file_descriptor = creat(fn, S_IRUSR | S_IWUSR)) < 0)
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perror("creat() error");
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/* create file to dup to */
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else if((file_descriptor2 = creat(fn2, S_IWUSR)) < 0)
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perror("creat()error");
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/* dup file_descriptor to file_descriptor2; print results */
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else {
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print_file_id(file_descriptor);
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print_file_id(file_descriptor2);
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if ((file_descriptor2 = dup2(file_descriptor, file_descriptor2)) < 0)
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perror("dup2() error");
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else {
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puts("After dup2()...");
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print_file_id(file_descriptor);
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|
print_file_id(file_descriptor2);
|
||
|
|
puts("The file descriptors are different but they");
|
||
|
|
puts("point to the same file which is different than");
|
||
|
|
puts("the file that the second file_descriptor originally pointed to.");
|
||
|
|
close(file_descriptor);
|
||
|
|
close(file_descriptor2);
|
||
|
|
}
|
||
|
|
unlink(fn);
|
||
|
|
unlink(fn2);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<p><strong>Output:</strong></p>
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
The file id of file_descriptor 0 is 30
|
||
|
|
The file id of file_descriptor 3 is 58
|
||
|
|
After dup2()...
|
||
|
|
The file id of file_descriptor 0 is 30
|
||
|
|
The file id of file_descriptor 3 is 30
|
||
|
|
The file descriptors are different, but they
|
||
|
|
point to the same file, which is different than
|
||
|
|
the file that the second file_descriptor originally pointed to.
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<hr>
|
||
|
|
API introduced: V3R1
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<center>
|
||
|
|
<table cellpadding="2" cellspacing="2">
|
||
|
|
<tr align="center">
|
||
|
|
<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
|
||
|
|
"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
</center>
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
|