Hide unpublished nodes

Hello,

I would like to hide not published node. I think to add condition here:

>
     //now write content only if necessary
      if (strlen($c) > 2){
      $content .= "<ul class=\"booktree\">\n". $c. "</ul>\n";
<

But I don't know how is the best to know if a node is published:
- $node=node_load($nid) and $node->status?
or
- SQL query ?

Thanks