📄 getsockopt.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>getsockopt</title></head><body bgcolor="white"><basefont size="3"> <a name="getsockopt"></a> <a name="tag_03_252"></a><!-- getsockopt --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_252_01"></a>NAME</h4><blockquote>getsockopt - get the socket options</blockquote><h4><a name="tag_03_252_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/sys/socket.h.html">sys/socket.h</a>><br><br> int getsockopt(int</tt> <i>socket</i><tt>, int</tt> <i>level</i><tt>, int</tt> <i>option_name,</i><tt><br> void *restrict</tt> <i>option_value</i><tt>, socklen_t *restrict</tt><i>option_len</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_252_03"></a>DESCRIPTION</h4><blockquote><p>The <i>getsockopt</i>() function manipulates options associated with a socket.</p><p>The <i>getsockopt</i>() function shall retrieve the value for the option specified by the <i>option_name</i> argument for thesocket specified by the <i>socket</i> argument. If the size of the option value is greater than <i>option_len</i>, the value storedin the object pointed to by the <i>option_value</i> argument shall be silently truncated. Otherwise, the object pointed to by the<i>option_len</i> argument shall be modified to indicate the actual length of the value.</p><p>The <i>level</i> argument specifies the protocol level at which the option resides. To retrieve options at the socket level,specify the <i>level</i> argument as SOL_SOCKET. To retrieve options at other levels, supply the appropriate level identifier forthe protocol controlling the option. For example, to indicate that an option is interpreted by the TCP (Transmission ControlProtocol), set <i>level</i> to IPPROTO_TCP as defined in the <a href="../basedefs/netinet/in.h.html"><i><netinet/in.h></i></a> header.</p><p>The socket in use may require the process to have appropriate privileges to use the <i>getsockopt</i>() function.</p><p>The <i>option_name</i> argument specifies a single option to be retrieved. It can be one of the following values defined in <ahref="../basedefs/sys/socket.h.html"><i><sys/socket.h></i></a>:</p><dl compact><dt>SO_DEBUG</dt><dd>Reports whether debugging information is being recorded. This option shall store an <b>int</b> value. This is a Booleanoption.</dd><dt>SO_ACCEPTCONN</dt><dd>Reports whether socket listening is enabled. This option shall store an <b>int</b> value. This is a Boolean option.</dd><dt>SO_BROADCAST</dt><dd>Reports whether transmission of broadcast messages is supported, if this is supported by the protocol. This option shall storean <b>int</b> value. This is a Boolean option.</dd><dt>SO_REUSEADDR</dt><dd>Reports whether the rules used in validating addresses supplied to <a href="../functions/bind.html"><i>bind</i>()</a> shouldallow reuse of local addresses, if this is supported by the protocol. This option shall store an <b>int</b> value. This is aBoolean option.</dd><dt>SO_KEEPALIVE</dt><dd>Reports whether connections are kept active with periodic transmission of messages, if this is supported by the protocol. <p>If the connected socket fails to respond to these messages, the connection shall be broken and threads writing to that socketshall be notified with a SIGPIPE signal. This option shall store an <b>int</b> value. This is a Boolean option.</p></dd><dt>SO_LINGER</dt><dd>Reports whether the socket lingers on <a href="../functions/close.html"><i>close</i>()</a> if data is present. If SO_LINGER isset, the system shall block the calling thread during <a href="../functions/close.html"><i>close</i>()</a> until it can transmitthe data or until the end of the interval indicated by the <i>l_linger</i> member, whichever comes first. If SO_LINGER is notspecified, and <a href="../functions/close.html"><i>close</i>()</a> is issued, the system handles the call in a way that allows thecalling thread to continue as quickly as possible. This option shall store a <b>linger</b> structure.</dd><dt>SO_OOBINLINE</dt><dd>Reports whether the socket leaves received out-of-band data (data marked urgent) inline. This option shall store an <b>int</b>value. This is a Boolean option.</dd><dt>SO_SNDBUF</dt><dd>Reports send buffer size information. This option shall store an <b>int</b> value.</dd><dt>SO_RCVBUF</dt><dd>Reports receive buffer size information. This option shall store an <b>int</b> value.</dd><dt>SO_ERROR</dt><dd>Reports information about error status and clears it. This option shall store an <b>int</b> value.</dd><dt>SO_TYPE</dt><dd>Reports the socket type. This option shall store an <b>int</b> value. Socket types are described in <a href="xsh_chap02_10.html#tag_02_10_06"><i>Socket Types</i></a>.</dd><dt>SO_DONTROUTE</dt><dd>Reports whether outgoing messages bypass the standard routing facilities. The destination shall be on a directly-connectednetwork, and messages are directed to the appropriate network interface according to the destination address. The effect, if any,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><dt>SO_RCVLOWAT</dt><dd>Reports the minimum number of bytes to process for socket input operations. The default value for SO_RCVLOWAT is 1. IfSO_RCVLOWAT is set to a larger value, blocking receive calls normally wait until they have received the smaller of the low watermark value or the requested amount. (They may return less than the low water mark if an error occurs, a signal is caught, or thetype of data next in the receive queue is different from that returned; for example, out-of-band data.) This option shall store an<b>int</b> value. Note that not all implementations allow this option to be retrieved.</dd><dt>SO_RCVTIMEO</dt><dd>Reports the timeout value for input operations. This option shall store a <b>timeval</b> structure with the number of secondsand microseconds specifying the limit on how long to wait for an input operation to complete. If a receive operation has blockedfor this much time without receiving additional data, it shall return with a partial count or <i>errno</i> set to [EAGAIN] or[EWOULDBLOCK] if no data was received. The default for this option is zero, which indicates that a receive operation shall not timeout. Note that not all implementations allow this option to be retrieved.</dd><dt>SO_SNDLOWAT</dt><dd>Reports the minimum number of bytes to process for socket output operations. Non-blocking output operations shall process nodata if flow control does not allow the smaller of the send low water mark value or the entire request to be processed. This optionshall store an <b>int</b> value. Note that not all implementations allow this option to be retrieved.</dd><dt>SO_SNDTIMEO</dt><dd>Reports the timeout value specifying the amount of time that an output function blocks because flow control prevents data frombeing sent. If a send operation has blocked for this time, it shall return with a partial count or with <i>errno</i> set to[EAGAIN] or [EWOULDBLOCK] if no data was sent. The default for this option is zero, which indicates that a send operation shall nottime out. The option shall store a <b>timeval</b> structure. Note that not all implementations allow this option to beretrieved.</dd></dl><p>For Boolean options, a zero value indicates that the option is disabled and a non-zero value indicates that the option isenabled.</p></blockquote><h4><a name="tag_03_252_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>getsockopt</i>() shall return 0; otherwise, -1 shall be returned and <i>errno</i> set to indicatethe error.</p></blockquote><h4><a name="tag_03_252_05"></a>ERRORS</h4><blockquote><p>The <i>getsockopt</i>() function shall fail if:</p><dl compact><dt>[EBADF]</dt><dd>The <i>socket</i> argument is not a valid file descriptor.</dd><dt>[EINVAL]</dt><dd>The specified option is invalid at the specified socket level.</dd><dt>[ENOPROTOOPT]</dt><dd>The option is not supported by the protocol.</dd><dt>[ENOTSOCK]</dt><dd>The <i>socket</i> argument does not refer to a socket.</dd></dl><p>The <i>getsockopt</i>() function may fail if:</p><dl compact><dt>[EACCES]</dt><dd>The calling process does not have the appropriate privileges.</dd><dt>[EINVAL]</dt><dd>The socket has been shut down.</dd><dt>[ENOBUFS]</dt><dd>Insufficient resources are available in the system to complete the function.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_252_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_252_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_252_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_252_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_252_10"></a>SEE ALSO</h4><blockquote><p><a href="bind.html"><i>bind</i>()</a>, <a href="close.html"><i>close</i>()</a>, <a href="endprotoent.html"><i>endprotoent</i>()</a>, <a href="setsockopt.html"><i>setsockopt</i>()</a>, <a href="socket.html"><i>socket</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/sys/socket.h.html"><i><sys/socket.h></i></a>, <a href="../basedefs/netinet/in.h.html"><i><netinet/in.h></i></a></p></blockquote><h4><a name="tag_03_252_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 6. Derived from the XNS, Issue 5.2 specification.</p><p>The <b>restrict</b> keyword is added to the <i>getsockopt</i>() prototype for alignment with the ISO/IEC 9899:1999standard.</p><p>IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/47 is applied, updating the description of SO_LINGER in theDESCRIPTION so that it blocks the calling thread rather than the process.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -