?? recvmsg.htm
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<div class="ref_head"> UDT Reference: Functions</div>
<h4 class="func_name"><strong>recvmsg</strong></h4>
<p>The <b>recvmsg</b> method receives a valid message.</p>
<div class="code">int recvmsg(<br />
UDTSOCKET <font color="#FFFFFF">u</font>,<br />
char* <font color="#FFFFFF">msg</font>,<br />
int <font color="#FFFFFF">len</font><br />
);</div>
<h5>Parameters</h5>
<dl>
<dt><i>u</i></dt>
<dd>[in] Descriptor identifying a connected socket.</dd>
<dt><em>msg</em></dt>
<dd>[out] The buffer used to store incoming message.</dd>
<dt><em>len</em></dt>
<dd>[in] Length of the buffer.</dd>
</dl>
<h5>Return Value</h5>
<p>On success, <b>recvmsg</b> returns the actual size of received message. Otherwise UDT::ERROR is returned and specific error information can be retrieved by <a
href="error.htm">getlasterror</a>. If UDT_RCVTIMEO is set to a positive value, zero will be returned if no message is received before the timer expires.</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>ECONNLOST</td>
<td>2001</td>
<td>connection has been broken and no data left in receiver buffer.</td>
</tr>
<tr>
<td>ENOCONN</td>
<td>2002</td>
<td><i>u</i> is not connected.</td>
</tr>
<tr>
<td>EINVSOCK</td>
<td>5004</td>
<td><i>u</i> is not an valid socket.</td>
</tr>
<tr>
<td>ESTREAMILL</td>
<td>5009</td>
<td>cannot use <i>recvmsg</i> in SOCK_STREAM mode.</td>
</tr>
<tr>
<td>EASYNCRCV</td>
<td>6002</td>
<td><i>u</i> is non-blocking (UDT_RCVSYN = false) but no message is available.</td>
</tr>
</table>
<h5>Description</h5>
<p>The <strong>recvmsg</strong> method reads a message from the protocol buffer. The UDT socket must be in SOCK_DGRAM mode in order to send or receive messages. Message is the minimum
data unit in this situation. Each <strong>recvmsg</strong> will read no more than one message, even if the message is smaller than the size of <i>buf</i> and there
are more messages available. On the other hand, if the <i>buf</i> is not enough to hold the first message, only part of the message will be copied into the buffer,
but the message will still be discarded after this <strong>recvmsg</strong> call.</p>
<p>In blocking mode (default), <strong>recvmsg</strong> waits until there is a valid message received into the receiver buffer. In non-blocking mode,
strong>recvmsg</strong> returns immediately and returns error if no message available.</p>
<p>If UDT_RCVTIMEO is set and the socket is in blocking mode, <strong>recvmsg</strong> only waits a limited time specified by UDT_RCVTIMEO option. If there is still
no message available when the timer expires, zero will be returned. UDT_RCVTIMEO has no effect for non-blocking socket.</p>
<h5>See Also</h5>
<p><strong><a href="select.htm">select</a>, <a href="sendmsg.htm">send</a></strong></p>
<p> </p>
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