291 lines
7.5 KiB
HTML
291 lines
7.5 KiB
HTML
<!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>pipe()--Create an Interprocess Channel</title>
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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</head>
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<body>
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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>pipe()--Create an Interprocess Channel</h2>
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<div class="box" style="width: 60%;">
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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 pipe(int <em>fildes[2]</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: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>pipe()</strong> function creates a data pipe and places two file
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descriptors, one each into the arguments <em>fildes[0]</em> and <em>
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fildes[1]</em>, that refer to the open file descriptions for the read and write
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ends of the pipe, respectively. Their integer values will be the two lowest
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available at the time of the <strong>pipe()</strong> call. The O_NONBLOCK and
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FD_CLOEXEC flags will be clear on both descriptors. NOTE: these flags can,
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however, be set by the <strong>fcntl()</strong> function.</p>
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<p>Data can be written to the file descriptor <em>fildes[1]</em> and read from
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file descriptor <em>fildes[0]</em>. A read on the file descriptor <em>
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fildes[0]</em> will access data written to the file descriptor <em>
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fildes[1]</em> on a first-in-first-out basis. File descriptor <em>
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fildes[0]</em> is open for reading only. File descriptor <em>fildes[1]</em> is
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open for writing only.</p>
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<p>The <strong>pipe()</strong> function is often used with the <strong>
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spawn()</strong> function to allow the parent and child processes to send data
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to each other.</p>
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<p>Upon successful completion, <strong>pipe()</strong> will update the access
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time, change time, and modification time of the pipe.</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[2]</em></strong></dt>
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<dd>(Output) An integer array of size 2 that will receive the pipe
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descriptors.</dd>
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</dl>
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<br>
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<h3>Authorities</h3>
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<p>None.</p>
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<br>
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<h3>Return Value</h3>
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<table cellpadding="5">
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<!-- cols="5 95" -->
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<tr>
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<td align="left" valign="top"><em>0</em></td>
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<td align="left" valign="top"><strong>pipe()</strong> was successful.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>-1</em></td>
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<td align="left" valign="top"><strong>pipe()</strong> was not successful. The
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<em>errno</em> variable is set to indicate the error.</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 Conditions</h3>
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<p>If <strong>pipe()</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#EFAULT">EFAULT</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#EMFILE">EMFILE</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#ENFILE">ENFILE</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#ENOMEM">ENOMEM</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#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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<h3><a name="USAGE_NOTES">Usage Notes</a></h3>
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<ol>
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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), the descriptors that are returned are scan descriptors. See
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<a href="ifsopenexit.htm">Integrated File System Scan on Open Exit Programs</a>
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and <a href="ifscloseexit.htm">Integrated File System Scan on Close Exit
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Programs</a> for more information. If a process is spawned, these scan
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descriptors are not inherited by the spawned process and therefore cannot be
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used in that spawned process. Therefore, in this case, the descriptors returned
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by <strong>pipe()</strong> function will only work within the same process.
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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>The <<strong>fcntl.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="fcntl.htm">fcntl()</a>--Perform File Control Command<br>
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</li>
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<li><a href="fstat.htm">fstat()</a>--Get File Information by Descriptor<br>
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</li>
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<li><a href="pipe.htm">Qp0zPipe()</a>--Create Interprocess Channel with
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Sockets<br>
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</li>
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<li><a href="read.htm">read()</a>--Read from Descriptor<br>
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</li>
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<li><a href="spawn.htm">spawn()</a>--Spawn Process<br>
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</li>
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<li><a href="write.htm">write()</a>--Write to Descriptor</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 creates a pipe, writes 10 bytes of data to the pipe,
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and then reads those 10 bytes of data from the pipe.</p>
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<pre>
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#include <stdio.h>
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#include <unistd.h>
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#include <string.h>
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void main()
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{
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int fildes[2];
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int rc;
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char writeData[10];
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char readData[10];
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int bytesWritten;
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int bytesRead;
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memset(writeData,'A',10);
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if (-1 == pipe(fildes))
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{
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perror("pipe error");
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return;
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}
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if (-1 == (bytesWritten = write(fildes[1],
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writeData,
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10)))
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{
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perror("write error");
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}
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else
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{
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printf("wrote %d bytes\n",bytesWritten);
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if (-1 == (bytesRead = read(fildes[0],
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readData,
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10)))
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{
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perror("read error");
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}
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else
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{
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printf("read %d bytes\n",bytesRead);
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}
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}
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close(fildes[0]);
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close(fildes[1]);
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return;
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}
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</pre>
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<br>
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<hr>
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API introduced: V5R1
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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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