r</span> 
<a name="idp57065120-bb"></a><span class="identifier">insert_before</span><span class="special">(</span><span class="identifier">node_ptr</span> header<span class="special">,</span> <span class="identifier">node_ptr</span> pos<span class="special">,</span> <span class="identifier">node_ptr</span> new_node<span class="special">)</span><span class="special">;</span></pre>
<p><span class="bold"><strong>Requires</strong></span>: "header" must be the header node of a tree. "pos" must be a valid iterato