274 lines
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274 lines
12 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>close</title>
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<basefont size="3"> <a name="close"></a> <a name="tag_03_80"></a><!-- close -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_80_01"></a>NAME</h4>
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<blockquote>close - close a file descriptor</blockquote>
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<h4><a name="tag_03_80_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br>
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<br>
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int close(int</tt> <i>fildes</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_80_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>close</i>() function shall deallocate the file descriptor indicated by <i>fildes</i>. To deallocate means to make the
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file descriptor available for return by subsequent calls to <a href="../functions/open.html"><i>open</i>()</a> or other functions
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that allocate file descriptors. All outstanding record locks owned by the process on the file associated with the file descriptor
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shall be removed (that is, unlocked).</p>
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<p>If <i>close</i>() is interrupted by a signal that is to be caught, it shall return -1 with <i>errno</i> set to [EINTR] and the
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state of <i>fildes</i> is unspecified. If an I/O error occurred while reading from or writing to the file system during
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<i>close</i>(), it may return -1 with <i>errno</i> set to [EIO]; if this error is returned, the state of <i>fildes</i> is
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unspecified.</p>
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<p>When all file descriptors associated with a pipe or FIFO special file are closed, any data remaining in the pipe or FIFO shall
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be discarded.</p>
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<p>When all file descriptors associated with an open file description have been closed, the open file description shall be
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freed.</p>
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<p>If the link count of the file is 0, when all file descriptors associated with the file are closed, the space occupied by the
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file shall be freed and the file shall no longer be accessible.</p>
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<p><sup>[<a href="javascript:open_code('XSR')">XSR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If a STREAMS-based <i>fildes</i> is closed and the calling process was previously registered to receive a SIGPOLL signal for events
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associated with that STREAM, the calling process shall be unregistered for events associated with the STREAM. The last
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<i>close</i>() for a STREAM shall cause the STREAM associated with <i>fildes</i> to be dismantled. If O_NONBLOCK is not set and
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there have been no signals posted for the STREAM, and if there is data on the module's write queue, <i>close</i>() shall wait for
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an unspecified time (for each module and driver) for any output to drain before dismantling the STREAM. The time delay can be
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changed via an I_SETCLTIME <a href="../functions/ioctl.html"><i>ioctl</i>()</a> request. If the O_NONBLOCK flag is set, or if there
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are any pending signals, <i>close</i>() shall not wait for output to drain, and shall dismantle the STREAM immediately.</p>
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<p>If the implementation supports STREAMS-based pipes, and <i>fildes</i> is associated with one end of a pipe, the last
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<i>close</i>() shall cause a hangup to occur on the other end of the pipe. In addition, if the other end of the pipe has been named
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by <a href="../functions/fattach.html"><i>fattach</i>()</a>, then the last <i>close</i>() shall force the named end to be detached
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by <a href="../functions/fdetach.html"><i>fdetach</i>()</a>. If the named end has no open file descriptors associated with it and
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gets detached, the STREAM associated with that end shall also be dismantled. <img src="../images/opt-end.gif" alt="[Option End]"
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border="0"></p>
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<p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If <i>fildes</i> refers to the master side of a pseudo-terminal, and this is the last close, a SIGHUP signal shall be sent to the
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process group, if any, for which the slave side of the pseudo-terminal is the controlling terminal. It is unspecified whether
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closing the master side of the pseudo-terminal flushes all queued input and output. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('XSR')">XSR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If <i>fildes</i> refers to the slave side of a STREAMS-based pseudo-terminal, a zero-length message may be sent to the master. <img
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src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('AIO')">AIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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When there is an outstanding cancelable asynchronous I/O operation against <i>fildes</i> when <i>close</i>() is called, that I/O
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operation may be canceled. An I/O operation that is not canceled completes as if the <i>close</i>() operation had not yet occurred.
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All operations that are not canceled shall complete as if the <i>close</i>() blocked until the operations completed. The
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<i>close</i>() operation itself need not block awaiting such I/O completion. Whether any I/O operation is canceled, and which I/O
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operation may be canceled upon <i>close</i>(), is implementation-defined. <img src="../images/opt-end.gif" alt="[Option End]"
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border="0"></p>
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<p><sup>[<a href="javascript:open_code('MF')">MF|SHM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If a shared memory object or a memory mapped file remains referenced at the last close (that is, a process has it mapped), then the
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entire contents of the memory object shall persist until the memory object becomes unreferenced. If this is the last close of a
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shared memory object or a memory mapped file and the close results in the memory object becoming unreferenced, and the memory
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object has been unlinked, then the memory object shall be removed. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></p>
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<p>If <i>fildes</i> refers to a socket, <i>close</i>() shall cause the socket to be destroyed. If the socket is in connection-mode,
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and the SO_LINGER option is set for the socket with non-zero linger time, and the socket has untransmitted data, then
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<i>close</i>() shall block for up to the current linger interval until all data is transmitted.</p>
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</blockquote>
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<h4><a name="tag_03_80_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, 0 shall be returned; otherwise, -1 shall be returned and <i>errno</i> set to indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_80_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>close</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EBADF]</dt>
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<dd>The <i>fildes</i> argument is not a valid file descriptor.</dd>
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<dt>[EINTR]</dt>
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<dd>The <i>close</i>() function was interrupted by a signal.</dd>
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</dl>
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<p>The <i>close</i>() function may fail if:</p>
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<dl compact>
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<dt>[EIO]</dt>
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<dd>An I/O error occurred while reading from or writing to the file system.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_80_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_80_06_01"></a>Reassigning a File Descriptor</h5>
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<p>The following example closes the file descriptor associated with standard output for the current process, re-assigns standard
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output to a new file descriptor, and closes the original file descriptor to clean up. This example assumes that the file descriptor
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0 (which is the descriptor for standard input) is not closed.</p>
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<pre>
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<tt>#include <unistd.h>
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...
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int pfd;
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...
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close(1);
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dup(pfd);
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close(pfd);
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...
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</tt>
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</pre>
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<p>Incidentally, this is exactly what could be achieved using:</p>
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<pre>
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<tt>dup2(pfd, 1);
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close(pfd);
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</tt>
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</pre>
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<h5><a name="tag_03_80_06_02"></a>Closing a File Descriptor</h5>
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<p>In the following example, <i>close</i>() is used to close a file descriptor after an unsuccessful attempt is made to associate
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that file descriptor with a stream.</p>
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<pre>
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<tt>#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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<br>
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#define LOCKFILE "/etc/ptmp"
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...
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int pfd;
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FILE *fpfd;
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...
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if ((fpfd = fdopen (pfd, "w")) == NULL) {
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close(pfd);
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unlink(LOCKFILE);
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exit(1);
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}
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...
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_80_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>An application that had used the <i>stdio</i> routine <a href="../functions/fopen.html"><i>fopen</i>()</a> to open a file should
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use the corresponding <a href="../functions/fclose.html"><i>fclose</i>()</a> routine rather than <i>close</i>(). Once a file is
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closed, the file descriptor no longer exists, since the integer corresponding to it no longer refers to a file.</p>
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</blockquote>
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<h4><a name="tag_03_80_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The use of interruptible device close routines should be discouraged to avoid problems with the implicit closes of file
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descriptors by <i><a href="../functions/exec.html">exec</a></i> and <a href="../functions/exit.html"><i>exit</i>()</a>. This volume
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of IEEE Std 1003.1-2001 only intends to permit such behavior by specifying the [EINTR] error condition.</p>
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</blockquote>
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<h4><a name="tag_03_80_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_80_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_06.html#tag_02_06"><i>STREAMS</i></a> , <a href="fattach.html"><i>fattach</i>()</a> , <a href=
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"fclose.html"><i>fclose</i>()</a> , <a href="fdetach.html"><i>fdetach</i>()</a> , <a href="fopen.html"><i>fopen</i>()</a> , <a
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href="ioctl.html"><i>ioctl</i>()</a> , <a href="open.html"><i>open</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_80_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_80_12"></a>Issue 5</h4>
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<blockquote>
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<p>The DESCRIPTION is updated for alignment with the POSIX Realtime Extension.</p>
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</blockquote>
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<h4><a name="tag_03_80_13"></a>Issue 6</h4>
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<blockquote>
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<p>The DESCRIPTION related to a STREAMS-based file or pseudo-terminal is marked as part of the XSI STREAMS Option Group.</p>
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<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
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<ul>
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<li>
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<p>The [EIO] error condition is added as an optional error.</p>
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</li>
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<li>
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<p>The DESCRIPTION is updated to describe the state of the <i>fildes</i> file descriptor as unspecified if an I/O error occurs and
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an [EIO] error condition is returned.</p>
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</li>
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</ul>
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<p>Text referring to sockets is added to the DESCRIPTION.</p>
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<p>The DESCRIPTION is updated for alignment with IEEE Std 1003.1j-2000 by specifying that shared memory objects and
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memory mapped files (and not typed memory objects) are the types of memory objects to which the paragraph on last closes
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applies.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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