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study/Ref-docs/POSIX/susv3/functions/getsockopt.html
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study/Ref-docs/POSIX/susv3/functions/getsockopt.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 name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>getsockopt</title>
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</head>
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<body bgcolor="white">
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<basefont size="3"> <a name="getsockopt"></a> <a name="tag_03_252"></a><!-- getsockopt -->
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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_252_01"></a>NAME</h4>
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<blockquote>getsockopt - get the socket options</blockquote>
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<h4><a name="tag_03_252_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/sys/socket.h.html">sys/socket.h</a>><br>
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<br>
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int getsockopt(int</tt> <i>socket</i><tt>, int</tt> <i>level</i><tt>, int</tt> <i>option_name,</i><tt><br>
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void *restrict</tt> <i>option_value</i><tt>, socklen_t *restrict</tt>
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<i>option_len</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_252_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>getsockopt</i>() function manipulates options associated with a socket.</p>
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<p>The <i>getsockopt</i>() function shall retrieve the value for the option specified by the <i>option_name</i> argument for the
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socket specified by the <i>socket</i> argument. If the size of the option value is greater than <i>option_len</i>, the value stored
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in the object pointed to by the <i>option_value</i> argument shall be silently truncated. Otherwise, the object pointed to by the
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<i>option_len</i> argument shall be modified to indicate the actual length of the value.</p>
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<p>The <i>level</i> argument specifies the protocol level at which the option resides. To retrieve options at the socket level,
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specify the <i>level</i> argument as SOL_SOCKET. To retrieve options at other levels, supply the appropriate level identifier for
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the protocol controlling the option. For example, to indicate that an option is interpreted by the TCP (Transmission Control
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Protocol), set <i>level</i> to IPPROTO_TCP as defined in the <a href=
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"../basedefs/netinet/in.h.html"><i><netinet/in.h></i></a> header.</p>
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<p>The socket in use may require the process to have appropriate privileges to use the <i>getsockopt</i>() function.</p>
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<p>The <i>option_name</i> argument specifies a single option to be retrieved. It can be one of the following values defined in <a
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href="../basedefs/sys/socket.h.html"><i><sys/socket.h></i></a>:</p>
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<dl compact>
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<dt>SO_DEBUG</dt>
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<dd>Reports whether debugging information is being recorded. This option shall store an <b>int</b> value. This is a Boolean
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option.</dd>
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<dt>SO_ACCEPTCONN</dt>
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<dd>Reports whether socket listening is enabled. This option shall store an <b>int</b> value. This is a Boolean option.</dd>
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<dt>SO_BROADCAST</dt>
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<dd>Reports whether transmission of broadcast messages is supported, if this is supported by the protocol. This option shall store
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an <b>int</b> value. This is a Boolean option.</dd>
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<dt>SO_REUSEADDR</dt>
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<dd>Reports whether the rules used in validating addresses supplied to <a href="../functions/bind.html"><i>bind</i>()</a> should
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allow reuse of local addresses, if this is supported by the protocol. This option shall store an <b>int</b> value. This is a
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Boolean option.</dd>
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<dt>SO_KEEPALIVE</dt>
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<dd>Reports whether connections are kept active with periodic transmission of messages, if this is supported by the protocol.
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<p>If the connected socket fails to respond to these messages, the connection shall be broken and threads writing to that socket
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shall be notified with a SIGPIPE signal. This option shall store an <b>int</b> value. This is a Boolean option.</p>
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</dd>
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<dt>SO_LINGER</dt>
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<dd>Reports whether the socket lingers on <a href="../functions/close.html"><i>close</i>()</a> if data is present. If SO_LINGER is
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set, the system blocks the process during <a href="../functions/close.html"><i>close</i>()</a> until it can transmit the data or
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until the end of the interval indicated by the <i>l_linger</i> member, whichever comes first. If SO_LINGER is not specified, and <a
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href="../functions/close.html"><i>close</i>()</a> is issued, the system handles the call in a way that allows the process to
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continue as quickly as possible. This option shall store a <b>linger</b> structure.</dd>
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<dt>SO_OOBINLINE</dt>
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<dd>Reports whether the socket leaves received out-of-band data (data marked urgent) inline. This option shall store an <b>int</b>
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value. This is a Boolean option.</dd>
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<dt>SO_SNDBUF</dt>
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<dd>Reports send buffer size information. This option shall store an <b>int</b> value.</dd>
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<dt>SO_RCVBUF</dt>
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<dd>Reports receive buffer size information. This option shall store an <b>int</b> value.</dd>
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<dt>SO_ERROR</dt>
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<dd>Reports information about error status and clears it. This option shall store an <b>int</b> value.</dd>
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<dt>SO_TYPE</dt>
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<dd>Reports the socket type. This option shall store an <b>int</b> value. Socket types are described in <a href=
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"xsh_chap02_10.html#tag_02_10_06"><i>Socket Types</i></a> .</dd>
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<dt>SO_DONTROUTE</dt>
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<dd>Reports whether outgoing messages bypass the standard routing facilities. The destination shall be on a directly-connected
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network, and messages are directed to the appropriate network interface according to the destination address. The effect, if any,
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of this option depends on what protocol is in use. This option shall store an <b>int</b> value. This is a Boolean option.</dd>
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<dt>SO_RCVLOWAT</dt>
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<dd>Reports the minimum number of bytes to process for socket input operations. The default value for SO_RCVLOWAT is 1. If
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SO_RCVLOWAT is set to a larger value, blocking receive calls normally wait until they have received the smaller of the low water
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mark value or the requested amount. (They may return less than the low water mark if an error occurs, a signal is caught, or the
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type of data next in the receive queue is different from that returned; for example, out-of-band data.) This option shall store an
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<b>int</b> value. Note that not all implementations allow this option to be retrieved.</dd>
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<dt>SO_RCVTIMEO</dt>
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<dd>Reports the timeout value for input operations. This option shall store a <b>timeval</b> structure with the number of seconds
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and microseconds specifying the limit on how long to wait for an input operation to complete. If a receive operation has blocked
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for this much time without receiving additional data, it shall return with a partial count or <i>errno</i> set to [EAGAIN] or
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[EWOULDBLOCK] if no data was received. The default for this option is zero, which indicates that a receive operation shall not time
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out. Note that not all implementations allow this option to be retrieved.</dd>
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<dt>SO_SNDLOWAT</dt>
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<dd>Reports the minimum number of bytes to process for socket output operations. Non-blocking output operations shall process no
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data if flow control does not allow the smaller of the send low water mark value or the entire request to be processed. This option
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shall store an <b>int</b> value. Note that not all implementations allow this option to be retrieved.</dd>
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<dt>SO_SNDTIMEO</dt>
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<dd>Reports the timeout value specifying the amount of time that an output function blocks because flow control prevents data from
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being sent. If a send operation has blocked for this time, it shall return with a partial count or with <i>errno</i> set to
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[EAGAIN] or [EWOULDBLOCK] if no data was sent. The default for this option is zero, which indicates that a send operation shall not
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time out. The option shall store a <b>timeval</b> structure. Note that not all implementations allow this option to be
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retrieved.</dd>
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</dl>
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<p>For Boolean options, a zero value indicates that the option is disabled and a non-zero value indicates that the option is
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enabled.</p>
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<p>Options at other protocol levels vary in format and name.</p>
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<p>The socket in use may require the process to have appropriate privileges to use the <i>getsockopt</i>() function.</p>
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</blockquote>
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<h4><a name="tag_03_252_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>getsockopt</i>() shall return 0; otherwise, -1 shall be returned and <i>errno</i> set to indicate
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the error.</p>
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</blockquote>
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<h4><a name="tag_03_252_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>getsockopt</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>socket</i> argument is not a valid file descriptor.</dd>
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<dt>[EINVAL]</dt>
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<dd>The specified option is invalid at the specified socket level.</dd>
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<dt>[ENOPROTOOPT]</dt>
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<dd><br>
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The option is not supported by the protocol.</dd>
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<dt>[ENOTSOCK]</dt>
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<dd>The <i>socket</i> argument does not refer to a socket.</dd>
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</dl>
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<p>The <i>getsockopt</i>() function may fail if:</p>
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<dl compact>
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<dt>[EACCES]</dt>
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<dd>The calling process does not have the appropriate privileges.</dd>
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<dt>[EINVAL]</dt>
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<dd>The socket has been shut down.</dd>
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<dt>[ENOBUFS]</dt>
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<dd>Insufficient resources are available in the system to complete the function.</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_252_06"></a>EXAMPLES</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_252_07"></a>APPLICATION USAGE</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_252_08"></a>RATIONALE</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_252_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_252_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="bind.html"><i>bind</i>()</a> , <a href="close.html"><i>close</i>()</a> , <a href=
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"endprotoent.html"><i>endprotoent</i>()</a> , <a href="setsockopt.html"><i>setsockopt</i>()</a> , <a href=
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"socket.html"><i>socket</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/socket.h.html"><i><sys/socket.h></i></a>, <a href=
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"../basedefs/netinet/in.h.html"><i><netinet/in.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_252_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 6. Derived from the XNS, Issue 5.2 specification.</p>
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<p>The <b>restrict</b> keyword is added to the <i>getsockopt</i>() prototype for alignment with the ISO/IEC 9899:1999
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standard.</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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]</font></center>
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