how to convert a boost::weak_ptr to a boost::shared_ptr
<p>i have a shared_ptr and a weak_ptr</p>

<pre><code>typedef boost::weak_ptr&lt;classname&gt; classnamePtr;
typedef boost::shared_ptr&lt;x&gt; xPtr;
</code></pre>

<p>how to convert a weak_ptr to a shared_ptr</p>

<pre><code>shared_ptr = weak_ptr;
Xptr = classnameptr; ?????
</code></pre>
