How to convert text with html tags into plain text in php

Tag phphtml

Such as the following text

Reply content:

preg_replace regular replacement
http://www.jb51.net/article/27706.htm

<code> <?php $s="<a>aaaa<b>bbbbb</b><font color="red">cc</font>";
echo $s."<br>";
$s= preg_replace("/]+>/is", "", $s);
echo $s;
?>
</code>