<?php $a=null; $b=‘‘; echo (isset($a))?"OK":"NG"; echo ‘<br>‘; echo (!empty($a))?"OK":"NG"; echo ‘<hr>‘; echo (isset($b))?"OK":"NG"; echo ‘<br>‘; echo (!empty($b))?"OK":"NG"; echo ‘<br>‘; /* NG NG OK NG */ ?>
原文：http://www.cnblogs.com/sky20080101/p/7065397.html