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---
version: tip
layout: manpage_v2
title: nng_log(3)
---
<h1>nng_log(3)</h1>
<div class="sect1">
<h2 id="_name">NAME</h2>
<div class="sectionbody">
<div class="paragraph">
<p>nng_log - log messages</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"><nng/nng.h></span>
<span class="tok-kt">void</span><span class="tok-w"> </span><span class="tok-nf">nng_log_err</span><span class="tok-p">(</span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msgid</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msg</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-p">...);</span>
<span class="tok-kt">void</span><span class="tok-w"> </span><span class="tok-nf">nng_log_warn</span><span class="tok-p">(</span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msgid</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msg</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-p">...);</span>
<span class="tok-kt">void</span><span class="tok-w"> </span><span class="tok-nf">nng_log_notice</span><span class="tok-p">(</span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msgid</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msg</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-p">...);</span>
<span class="tok-kt">void</span><span class="tok-w"> </span><span class="tok-nf">nng_log_info</span><span class="tok-p">(</span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msgid</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msg</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-p">...);</span>
<span class="tok-kt">void</span><span class="tok-w"> </span><span class="tok-nf">nng_log_debug</span><span class="tok-p">(</span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msgid</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msg</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-p">...);</span>
<span class="tok-kt">void</span><span class="tok-w"> </span><span class="tok-nf">nng_log_auth</span><span class="tok-p">(</span><span class="tok-n">nng_log_level</span><span class="tok-w"> </span><span class="tok-n">level</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msgid</span><span class="tok-p">,</span><span class="tok-w"> </span><span class="tok-k">const</span><span class="tok-w"> </span><span class="tok-kt">char</span><span class="tok-w"> </span><span class="tok-o">*</span><span class="tok-n">msg</span><span class="tok-p">,</span><span class="tok-w"> </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>These functions are used to post a message to system or application logs.</p>
</div>
<div class="paragraph">
<p>The first five forms all post a message at the severity indicated by the function name.
The <em>msgid</em> should be a short message identifier that should indicate the message in question.
A <code>NULL</code> value for <em>msgid</em> canbe used as well.</p>
</div>
<div class="paragraph">
<p>Message identifiers can be used to assist in filtering logs.
These should uniquely identify the nature of the problem, whe possible, to assist in trouble-shooting.
They should also be short.
Eight characters or less is ideal, and more than sixteen is strongly discouraged.</p>
</div>
<div class="paragraph">
<p>The message is formatting as if by <code>sprintf</code>, using <code>msg</code> as the format, and remaining arguments as arguments to the format.</p>
</div>
<div class="paragraph">
<p>The final function, <code>nng_log_auth</code>, is used for posting authentication related messages which might be treated specially, such as be storing them in a separate secured log file.
It takes the severity as a level in <em>level</em>.
The severity can be one of the following values:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><code>NNG_LOG_ERR</code></p>
</li>
<li>
<p><code>NNG_LOG_WARN</code></p>
</li>
<li>
<p><code>NNG_LOG_NOTICE</code></p>
</li>
<li>
<p><code>NNG_LOG_INFO</code></p>
</li>
<li>
<p><code>NNG_LOG_DEBUG</code></p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The message itself is handled according to the logging facility set up with <a href="nng_mg_set_logger.3.html"><code>nng_log_set_logger</code></a>.
Message delivery is best effort, and messages may be suppressed based on the priority set with <a href="nng_log_set_level.3.html"><code>nng_log_set_level</code></a>.</p>
</div>
<div class="paragraph">
<p>Note that in order to get log messages, a suitable logger must be set using <code>nng_log_set_logger</code>.
The default logger, <code>nng_null_logger</code> simply discards logged content.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph">
<p><a href="nng_log_set_facility.3.html">nng_log_set_facility(3)</a>,
<a href="nng_log_set_level.3.html">nng_log_set_level(3)</a>,
<a href="nng_log_set_logger.3.html">nng_log_set_logger(3)</a></p>
</div>
</div>
</div>
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