C++ exception. But if the <a class="link" href="../policy.html" title="Chapter&#160;18.&#160;Policies: Controlling Precision, Error Handling etc">Policy</a> is to ignore
      the error, or set global <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code>,
      then a NaN will be returned.
    </p>
<p>
      This behaviour is chosen to assist compatibility with the behaviour of <span class="emphasis"><em>ISO/IEC
      9899:1999 Programming languages - C</em