117 lines
4.5 KiB
HTML
117 lines
4.5 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>lseek64()--Set File Read/Write Offset (Large File Enabled)</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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<!-- file cleaned -->
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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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<!-- This file has undergone html cleanup May 2002 by JET -->
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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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<!--End Header Records --><!-- 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>lseek64()--Set File Read/Write Offset (Large File Enabled)</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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off64_t lseek64(int <em>file_descriptor</em>,
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off64_t <em>offset</em>, int <em>whence)</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>lseek64()</strong> function changes the current file offset to a
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new position in the file. The new position is the given byte <em>offset</em>
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from the position specified by <em>whence</em>. After you have used <strong>
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lseek64()</strong> to seek to a new location, the next I/O operation on the
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file begins at that location.</p>
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<p><strong>lseek64()</strong> lets you specify new file offsets past the
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current end of the file. If data is written at such a point, read operations in
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the gap between this data and the old end of the file will return bytes
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containing binary zeros (or bytes containing blanks in the QSYS.LIB or
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independent ASP QSYS.LIB file systems). In other words, the gap is assumed to
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be filled with zeros (or with blanks in the QSYS.LIB or independent ASP
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QSYS.LIB file systems). If you seek past the end of a file, however, the length
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of the file is not automatically extended. The maximum offset that can be
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specified is the largest value that can be held in an 8-byte, signed integer.
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You must do a write operation before the file is actually extended.</p>
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<p>In the QSYS.LIB or independent ASP QSYS.LIB file systems, you can seek only
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to the beginning of a member while in text mode.</p>
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<p><strong>lseek64()</strong> is enabled for large files. It is capable of
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operating on files larger than 2GB minus 1 byte as long as the file has been
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opened by either of the following:</p>
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<ul compact>
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<li>Using the <strong>open64()</strong> function (see <a href="open64.htm">
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open64()--Open File (Large File Enabled)</a>).</li>
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<li>Using the <strong>open()</strong> function (see <a href="open.htm">
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open()--Open File</a>) with the O_LARGEFILE flag set.</li>
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</ul>
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<p>For additional information about parameters, authorities required, error
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conditions and examples, see <a href="lseek.htm">lseek()--Set File Read/Write
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Offset</a>.</p>
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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>When you develop in C-based languages, the prototypes for the 64-bit APIs
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are normally hidden. To use the <strong>lseek64()</strong> API and the off64_t
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data type, you must compile the source with the _LARGE_FILE_API defined.<br>
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</li>
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<li>All of the usage notes for <strong>lseek()</strong> apply to <strong>
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lseek64()</strong>. See <a href="lseek.htm#HDRLSKUSAG">Usage Notes</a> in the
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<strong>lseek()</strong> API.</li>
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</ol>
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<br>
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<hr>
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API introduced: V4R4
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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