get automatically assigned key when setting array value
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/3275082/php-get-index-of-last-inserted-item-in-array">PHP get index of last inserted item in array</a>  </p>
</blockquote>



<p>My array is generated the following way:</p>

<pre><code>$_SESSION['add_fail_urls'][] = $_REQUEST['url'];
</code></pre>

<p>How do I get a number value of the automatically assigned key <code>[]</code>?</p>
