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<body class="manpage">
<div id="header">
<h1>
nn_recv(3) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>nn_recv -
   receive a message
</p>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="paragraph"><p><strong>#include &lt;nanomsg/nn.h&gt;</strong></p></div>
<div class="paragraph"><p><strong>int nn_recv (int <em>s</em>, void <em>*buf</em>, size_t <em>len</em>, int <em>flags</em>);</strong></p></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph"><p>Receive a message from the socket <em>s</em> and store it in the buffer referenced by
the <em>buf</em> argument. Any bytes exceeding the length specified by the <em>len</em>
argument will be truncated.</p></div>
<div class="paragraph"><p>Alternatively, <em>nanomsg</em> can allocate the buffer for you. To do so,
let the <em>buf</em> parameter be a pointer to a void* variable (pointer to pointer)
to the receive buffer and set the <em>len</em> parameter to <em>NN_MSG</em>. If the call is
successful the user is responsible for deallocating the message using
the <a href="nn_freemsg.3.html">nn_freemsg(3)</a> function.</p></div>
<div class="paragraph"><p>The <em>flags</em> argument is a combination of the flags defined below:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>NN_DONTWAIT</strong>
</dt>
<dd>
<p>
Specifies that the operation should be performed in non-blocking mode. If the
message cannot be received straight away, the function will fail with <em>errno</em>
set to EAGAIN.
</p>
</dd>
</dl></div>
</div>
</div>
<div class="sect1">
<h2 id="_return_value">RETURN VALUE</h2>
<div class="sectionbody">
<div class="paragraph"><p>If the function succeeds number of bytes in the message is returned. Otherwise,
-1 is returned and <em>errno</em> is set to to one of the values defined
below.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_errors">ERRORS</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>EBADF</strong>
</dt>
<dd>
<p>
The provided socket is invalid.
</p>
</dd>
<dt class="hdlist1">
<strong>ENOTSUP</strong>
</dt>
<dd>
<p>
The operation is not supported by this socket type.
</p>
</dd>
<dt class="hdlist1">
<strong>EFSM</strong>
</dt>
<dd>
<p>
The operation cannot be performed on this socket at the moment because socket is
not in the appropriate state.  This error may occur with socket types that
switch between several states.
</p>
</dd>
<dt class="hdlist1">
<strong>EAGAIN</strong>
</dt>
<dd>
<p>
Non-blocking mode was requested and there&#8217;s no message to receive at the moment.
</p>
</dd>
<dt class="hdlist1">
<strong>EINTR</strong>
</dt>
<dd>
<p>
The operation was interrupted by delivery of a signal before the message was
received.
</p>
</dd>
<dt class="hdlist1">
<strong>ETIMEDOUT</strong>
</dt>
<dd>
<p>
Individual socket types may define their own specific timeouts. If such timeout
is hit this error will be returned.
</p>
</dd>
<dt class="hdlist1">
<strong>ETERM</strong>
</dt>
<dd>
<p>
The library is terminating.
</p>
</dd>
</dl></div>
</div>
</div>
<div class="sect1">
<h2 id="_examples">EXAMPLES</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
Receiving a message into a buffer allocated by the user
</dt>
<dd>
<p>
This example code will retrieve a message of either 100 bytes or less. If a
larger message was sent it will be truncated to 100 bytes.
</p>
</dd>
</dl></div>
<div class="listingblock">
<div class="content">
<pre><tt>char buf [100];
nbytes = nn_recv (s, buf, sizeof (buf), 0);</tt></pre>
</div></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Receiving a message into a buffer allocated by <em>nanomsg</em>
</dt>
<dd>
<p>
The following will get a message from the pipe with a buffer allocated by
the system. It is large enough to accommodate the entire message. This is a good
way to get the entire message without truncating if the size of the message is
unknown. It is the user&#8217;s responsibility to call <a href="nn_freemsg.3.html">nn_freemsg(3)</a> after
processing the message.
</p>
</dd>
</dl></div>
<div class="listingblock">
<div class="content">
<pre><tt>void *buf = NULL;
nbytes = nn_recv (s, &amp;buf, NN_MSG, 0);

if (nbytes &lt; 0) {
    /* handle error */
    ...
}
else {
    /* process message */
    ...
    nn_freemsg (buf);
}</tt></pre>
</div></div>
<div class="paragraph"><p>Note that this can be more efficient than manually allocating a buffer since
it is a zero-copy operation.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="nn_send.3.html">nn_send(3)</a>
<a href="nn_recvmsg.3.html">nn_recvmsg(3)</a>
<a href="nn_socket.3.html">nn_socket(3)</a>
<a href="nanomsg.7.html">nanomsg(7)</a></p></div>
</div>
</div>
<div class="sect1">
<h2 id="_authors">AUTHORS</h2>
<div class="sectionbody">
<div class="paragraph"><p>Martin Sustrik &lt;<a href="mailto:sustrik@250bpm.com">sustrik@250bpm.com</a>&gt;</p></div>
</div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
nanomsg 0.5-beta<br />
Last updated 2014-11-14 22:43:29 CET
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