 key_type &amp;x,
    bool readonly=false)
 </pre>
        <p>Find the greatest key less than or equal to x. </p>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idp50497680"></a>Parameters</h4>
              </div>
            </div>
          </div>
          <div class="sect4" lang="en" xml:lang="en">
            <div class="titlepage">
              <div>
                <div>
           