nism is as follows:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Inside <code>func</code>, the only interesting member of the structure
given by <code>opt</code> is the void pointer <code>opt-&gt;value</code>.
<code>*opt-&gt;value</code> will be the value that is saved into <code>var</code>, if you
use <code>OPT_CALLBACK()</code>.
For example, do <code>*(unsigned long *)opt-&gt;value = 42;</code> to get 42
into an <code>unsigned long</code> variable.</p>
</li>
<li>
<p>Return value <code>0</code> indicates su