161 lines
5.1 KiB
HTML
161 lines
5.1 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>pwrite64()--Write to Descriptor with 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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<!-- 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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<!-- 010308 JTROUS Creation date based on pwrite, for V5R2, DCR 98686 -->
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<!-- 011022 JTROUS Changes from API Review 1, V5R2 -->
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<!-- 030730 VONBERGE Remove QSYS.LIB comment about offset/text mode. -->
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<!-- It was moved to file system diffs in pwrite.htm. -->
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<!-- This file has undergone html cleanup May 2002 by JET -->
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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 id="HDRPWRITE64">pwrite64()--Write to Descriptor with Offset (large file
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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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ssize_t pwrite64
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(int <em>file_descriptor</em>, const void <em>*buf</em>,
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size_t <em>nbyte</em>, off64_t <em>offset</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>pwrite64()</strong> function writes <em>nbyte</em> bytes from
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<em>buf</em> to the file associated with <em>file_descriptor</em>. The <em>
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offset</em> value defines the starting position in the file and the file
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pointer position is not changed.</p>
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<p>The <em>offset</em> will also be ignored if <em>file_descriptor</em> refers
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to a descriptor obtained using the <strong>open()</strong> function with
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O_APPEND specified.</p>
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<p><strong>pwrite64()</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>
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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 O_LARGEFILE set in the oflag parameter.</li>
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</ul>
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<p>For additional information about parameters, authorities, and error
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conditions, see <a href="pwrite.htm">pwrite()--Write to Descriptor with
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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>pwrite64</strong> API, you must compile
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the source with the _LARGE_FILE_API macro defined.</li>
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<li>All of the usage notes for <strong>pwrite()</strong> apply to <strong>
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pwrite64()</strong>. See <em>Usage Notes</em> in the <strong>pwrite</strong>
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API.</li>
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</ol>
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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 writes a specific number of bytes to a file:</p>
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<pre>
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#define _LARGE_FILE_API
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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 <stdlib.h>
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#define mega_string_len 1000000
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main() {
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char *mega_string;
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int file_descriptor;
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int ret;
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off64_t off=5;
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char fn[]="write.file";
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if ((mega_string = (char*) malloc(mega_string_len+off)) == NULL)
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perror("malloc() error");
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else if ((file_descriptor = creat64(fn, S_IWUSR)) < 0)
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perror("creat64() error");
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else {
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memset(mega_string, '0', mega_string_len);
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if ((ret = pwrite64(file_descriptor, mega_string, mega_string_len, off)) == -1)
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perror("pwrite64() error");
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else printf("pwrite64() wrote %d bytes at offset %d\n", ret, off);
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if (close(file_descriptor)!= 0)
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perror("close() error");
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if (unlink(fn)!= 0)
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perror("unlink() error");
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}
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free(mega_string);
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}
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</pre>
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<p><strong>Output:</strong></p>
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<pre>
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pwrite64() wrote 1000000 bytes at offset 5
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</pre>
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<hr>
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API introduced: V5R2
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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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