entifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;(</span><span class="number">255</span><span class="special">).</span><span class="identifier">value_or</span><span class="special">(</span><span class="string">"bad"</span><span class="special">);</span>

<span class="comment">// 'i' and 's' are converted using boost::cnv::cstream</span>
<span class="comment">// with std::uppercase and std::hex formatting applied.</span>

<span class="identifi