📄 select.htm
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /><title> UDT Reference</title><link rel="stylesheet" href="udtdoc.css" type="text/css" /></head><body><div class="ref_head"> UDT Reference: Functions</div><h4 class="func_name"><strong>select</strong></h4><p>The <b>select</b> method queries one or more groups of UDT sockets.</p><div class="code">int select(<br /> int <font color="#FFFFFF">nfds</font>,<br /> UDSET* <font color="#FFFFFF">readfds</font>,<br /> UDSET* <font color="#FFFFFF">writefds</font>,<br /> UDSET* <font color="#FFFFFF">exceptfds</font>,<br /> const struct timeval* <font color="#FFFFFF">timeout</font><br />);</div><h5>Parameters</h5><dl> <dt><i>nfds</i></dt> <dd>[in] Ignored. For compatibility only.</dd> <dt><em>readfds</em></dt> <dd>[in, out] Optional pointer to a set of sockets to be checked for readability.</dd> <dt><em>writefds</em></dt> <dd>[in, out] Optional pointer to a set of sockets to be checked for writability.</dd> <dt><em>exceptfds</em></dt> <dd>[in, out] Ignored. For compatibility only.</dd> <dt><em>timeout</em></dt> <dd>[in] The future time when this call should be timeout.</dd></dl><h5>Return Value</h5><p>If any of the read or write query is positive, <strong>select</strong> returns the number of UDT sockets that are read for read/write. If no socket is ready before timeout, zero is returned. If there is any error, UDT::ERROR is returned and the specific error information can be retrieved using <a href="error.htm">getlasterror</a>. The <i>readfds</i> and/or <i>writefds</i> will be updated to contain the ready sockets only.</p><table width="100%" border="1" cellpadding="2" cellspacing="0" bordercolor="#CCCCCC"> <tr> <td width="17%" class="table_headline"><strong>Error Name</strong></td> <td width="17%" class="table_headline"><strong>Error Code</strong></td> <td width="83%" class="table_headline"><strong>Comment</strong></td> </tr> <tr> <td>EINVPARAM</td> <td>5003</td> <td>All three socket sets are empty or at least one of the socket is invalid.</td> </tr></table><h5>Description</h5><p>The UDSET is a structure to store the UDT socket descriptors. If should only be processed with the following macros.</p><dl> <dt><b>UD_CLR</b>(<i>u, *set</i>)</dt> <dd>Removes the descriptor <i>u</i> from <i>set</i>.</dd> <dt><b>UD_ISSET</b>(<i>u, *set</i>)</dt> <dd>Nonzero if <i>u</i> is a member of <i>set</i>; otherwise zero.</dd> <dt><b>UD_SET</b>(<i>u, *set</i>)</dt> <dd>Add descriptor <i>u</i> to <i>set</i>.</dd> <dt><b>UD_ZERO</b>(<i>*set</i>)</dt> <dd>Initialize <i>set</i> to an empty set.</dd></dl><p>The UDT descriptors sets originaly contains the sockets whose status is to be queried. When <strong>select</strong> returns, the descriptors sets only contain the sockets that are ready for IO. UD_ISSET can be used to check which one is ready.</p><p><i>readfds</i> is used to detect if any socket in this set is available for reading (recv, recvmsg), for accepting a new connection (accept), or the associated connection is broken. <i>writefds</i> is used to detect if any socket in this set has available buffer for sending (send, sendmsg). Currently <i>exceptfds</i> is not used.</p><h5>Example</h5><p>The following example shows how to check if a UDT socket is available for <strong>recv</strong>.</p><div class="code"><p>UDTSOCKET u;<br>...<br><br>timeval tv;<br>UDSET readfds;<br><br>tv.tv_sec = 1;<br>tv.tv_usec = 0;<br><br>UD_ZERO(&readfds);<br>UD_SET(u, &readfds);<br><br>int res = UDT::select(0, &readfds, NULL, NULL, &tv);<br><br>if ((res != UDT::ERROR) && (UD_ISSET(u, &readfds)))<br> // read data from u.<br>else<br> // timeout or error<br></p></div><p> </p></body></html>⌨️ 快捷键说明
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