<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation"> <title>pwrite64()--Write to Descriptor with Offset (large file enabled)</title> <!-- Begin Header Records --> <!-- All rights reserved. Licensed Materials Property of IBM --> <!-- US Government Users Restricted Rights --> <!-- Use, duplication or disclosure restricted by --> <!-- GSA ADP Schedule Contract with IBM Corp. --> <!-- Change History: --> <!-- YYMMDD USERID Change description --> <!-- Unix2 SCRIPT J converted by B2H R4.1 (346) (CMS) by V2KEA304 --> <!-- at RCHVMW2 on 17 Feb 1999 at 11:05:09 --> <!-- 010308 JTROUS Creation date based on pwrite, for V5R2, DCR 98686 --> <!-- 011022 JTROUS Changes from API Review 1, V5R2 --> <!-- 030730 VONBERGE Remove QSYS.LIB comment about offset/text mode. --> <!-- It was moved to file system diffs in pwrite.htm. --> <!-- This file has undergone html cleanup May 2002 by JET --> <!-- End Header Records --> <link rel="stylesheet" type="text/css" href="../rzahg/ic.css"> </head> <body> <!-- Java sync-link --> <script language="Javascript" src="../rzahg/synch.js" type="text/javascript"> </script> <a name="Top_Of_Page"></a> <h2 id="HDRPWRITE64">pwrite64()--Write to Descriptor with Offset (large file enabled)</h2> <div class="box" style="width: 70%;"> <br> Syntax<br> <pre> #include <unistd.h> ssize_t pwrite64 (int <em>file_descriptor</em>, const void <em>*buf</em>, size_t <em>nbyte</em>, off64_t <em>offset</em>); </pre> Service Program Name: QP0LLIB1<br> <!-- iddvc RMBR --> <br> Default Public Authority: *USE<br> <!-- iddvc RMBR --> <br> Threadsafe: Conditional; see <a href="#USAGE_NOTES">Usage Notes</a>.<br> <!-- iddvc RMBR --> <br> </div> <p>The <strong>pwrite64()</strong> function writes <em>nbyte</em> bytes from <em>buf</em> to the file associated with <em>file_descriptor</em>. The <em> offset</em> value defines the starting position in the file and the file pointer position is not changed.</p> <p>The <em>offset</em> will also be ignored if <em>file_descriptor</em> refers to a descriptor obtained using the <strong>open()</strong> function with O_APPEND specified.</p> <p><strong>pwrite64()</strong> is enabled for large files. It is capable of operating on files larger than 2GB minus 1 byte as long as the file has been opened by either of the following:</p> <ul> <li>Using the <strong>open64()</strong> function (see <a href="open64.htm"> open64()--Open File (large file enabled)</a>).</li> <li>Using the <strong>open()</strong> function (see <a href="open.htm"> open()--Open File</a>) with O_LARGEFILE set in the oflag parameter.</li> </ul> <p>For additional information about parameters, authorities, and error conditions, see <a href="pwrite.htm">pwrite()--Write to Descriptor with Offset</a>.</p> <br> <h3><a name="usage_notes">Usage Notes</a></h3> <ol type="1"> <li>When you develop in C-based languages, the prototypes for the 64-bit APIs are normally hidden. To use the <strong>pwrite64</strong> API, you must compile the source with the _LARGE_FILE_API macro defined.</li> <li>All of the usage notes for <strong>pwrite()</strong> apply to <strong> pwrite64()</strong>. See <em>Usage Notes</em> in the <strong>pwrite</strong> API.</li> </ol> <br> <h3>Example</h3> <p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a> for information pertaining to code examples.</p> <p>The following example writes a specific number of bytes to a file:</p> <pre> #define _LARGE_FILE_API #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #define mega_string_len 1000000 main() { char *mega_string; int file_descriptor; int ret; off64_t off=5; char fn[]="write.file"; if ((mega_string = (char*) malloc(mega_string_len+off)) == NULL) perror("malloc() error"); else if ((file_descriptor = creat64(fn, S_IWUSR)) < 0) perror("creat64() error"); else { memset(mega_string, '0', mega_string_len); if ((ret = pwrite64(file_descriptor, mega_string, mega_string_len, off)) == -1) perror("pwrite64() error"); else printf("pwrite64() wrote %d bytes at offset %d\n", ret, off); if (close(file_descriptor)!= 0) perror("close() error"); if (unlink(fn)!= 0) perror("unlink() error"); } free(mega_string); } </pre> <p><strong>Output:</strong></p> <pre> pwrite64() wrote 1000000 bytes at offset 5 </pre> <hr> API introduced: V5R2 <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>