t already exists when 
         <a class="xref" href="envopen.html" title="DB_ENV-&gt;open()">DB_ENV-&gt;open()</a>  is called, the
         information specified to <code class="methodname">DB_ENV-&gt;add_data_dir()</code> must be consistent
         with the existing environment or corruption can occur.
    </p>
      <p>
         The <code class="methodname">DB_ENV-&gt;add_data_dir()</code> <span>
            <span>
                  method returns a non-zero error value on failure and 0 on success.
    