man/tip/nn_cmsg.3compat.html


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---
version: tip
layout: manpage_v2
title: nn_cmsg(3compat)
---
<h1>nn_cmsg(3compat)</h1>
<div class="sect1">
<h2 id="_name">NAME</h2>
<div class="sectionbody">
<div class="paragraph">
<p>nn_cmsg - message control data (compatible API)</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content">
<pre class="pygments highlight"><code data-lang="c"><span></span><span class="tok-cp">#include</span><span class="tok-w"> </span><span class="tok-cpf">&lt;nanomsg/nn.h&gt;</span>

<span class="tok-k">struct</span><span class="tok-w"> </span><span class="tok-nc">nn_cmsghdr</span><span class="tok-w"> </span><span class="tok-p">{</span>
<span class="tok-w">    </span><span class="tok-kt">size_t</span><span class="tok-w"> </span><span class="tok-n">cmsg_len</span><span class="tok-p">;</span>
<span class="tok-w">    </span><span class="tok-kt">int</span><span class="tok-w">    </span><span class="tok-n">cmsg_level</span><span class="tok-p">;</span>
<span class="tok-w">    </span><span class="tok-kt">int</span><span class="tok-w">    </span><span class="tok-n">cmsg_type</span><span class="tok-p">;</span>
<span class="tok-p">};</span></code></pre>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The <code>nn_cmsghdr</code> structure describes a block of control data that is
associated with a message either sent by <a href="nn_sendmsg.3compat.html"><code>nn_sendmsg()</code></a>
or received by <a href="nn_recvmsg.3compat.html"><code>nn_recvmsg()</code></a>.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
This structure and supporting macros are provided for API
<a href="nng_compat.3compat.html">compatibility</a> with legacy <em>libnanomsg</em>.
Consider using the relevant <a href="libnng.3.html">modern API</a> instead.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Each header is followed by <code>cmsg_len</code> bytes of data, plus any padding required
to align the structure.</p>
</div>
<div class="paragraph">
<p>The only defined ancillary data at this time is the protocol headers used by
the protocols.
This uses <code>cmsg_level</code> set to <code>PROTO_SP</code> and the <code>cmsg_type</code> set to
<code>SP_HDR</code>.
The actual data for this will vary from depending on the protocol used.</p>
</div>
<div class="paragraph">
<p>Convenience macros are provided to make working with these fields easier.</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>struct nn_cmsghdr *NN_CMSG_FIRSTHDR(struct nn_msghdr *<em>hdr</em>)</code></dt>
<dd>
<p>This macro returns the first <code>struct nn_cmsghdr</code> header in <em>hdr</em>.</p>
</dd>
<dt class="hdlist1"><code>struct nn_cmsghdr *NN_CMSG_NXTHDR(struct nn_msghdr *<em>hdr</em>, struct nn_cmsghdr *<em>ch</em>)</code></dt>
<dd>
<p>This macro returns a pointer to the next <code>struct nn_cmsghdr</code> in <em>hdr</em> after <em>ch</em>.</p>
</dd>
<dt class="hdlist1"><code>void *NN_CMSG_DATA(struct nn_cmsghdr *<em>ch</em>)</code></dt>
<dd>
<p>This macro returns a pointer to the header-specific data for <em>ch</em>.</p>
</dd>
<dt class="hdlist1"><code>size_t NN_CMSG_ALIGN(size_t <em>len</em>)</code></dt>
<dd>
<p>This macro returns the length specified by <em>len</em>, plus any padding required to
provide the necessary alignment for another structure.</p>
</dd>
<dt class="hdlist1"><code>size_t NN_CMSG_SPACE(size_t <em>len</em>)</code></dt>
<dd>
<p>This macro returns the amount of space required for a header, with <em>len</em>
bytes of following data, and any necessary padding.</p>
</dd>
<dt class="hdlist1"><code>size_t NN_CMSG_LEN(size_t <em>len</em>)</code></dt>
<dd>
<p>This macro evaluates to the length of the header (including alignment),
and the associated data of length <em>len</em>, but without any trailing padding
to align for another header.</p>
</dd>
</dl>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph text-left">
<p><a href="nn_recvmsg.3compat.html">nn_recvmsg(3compat)</a>,
<a href="nn_sendmsg.3compat.html">nn_sendmsg(3compat)</a>,
<a href="nng_compat.3compat.html">nng_compat(3compat)</a>,
<a href="nng.7.html">nng(7)</a></p>
</div>
</div>
</div>