php过滤特殊字符实用函数

<?php
//特殊字符过滤
function htmldecode($str) 
{ 
if(empty($str)) return; 
if($str=="") return $str; 
$str=str_replace("&",chr(34),$str); 
$str=str_replace(">",">",$str); 
$str=str_replace("<","<",$str); 
$str=str_replace("&","&",$str); 
$str=str_replace(" ",chr(32),$str); 
$str=str_replace(" ",chr(9),$str); 
$str=str_replace("'",chr(39),$str); 
$str=str_replace("<br />",chr(13),$str); 
$str=str_replace("''","'",$str); 
$str=str_replace("select","select",$str); 
$str=str_replace("join","join",$str); 
$str=str_replace("union","union",$str); 
$str=str_replace("where","where",$str); 
$str=str_replace("insert","insert",$str); 
$str=str_replace("delete","delete",$str); 
$str=str_replace("update","update",$str); 
$str=str_replace("like","like",$str); 
$str=str_replace("drop","drop",$str); 
$str=str_replace("create","create",$str); 
$str=str_replace("modify","modify",$str); 
$str=str_replace("rename","rename",$str); 
$str=str_replace("alter","alter",$str); 
$str=str_replace("cas","cast",$str); 
//脚本学堂 http://www.jb200.com
$farr = array(  
"//s+/" , //过滤多余的空白  
"/<(//?)(img|script|i?frame|style|html|body|title|link|meta|/?|/%)([^>]*?)>/isu" , //过滤 <script 防止引入恶意内容或恶意代码,如果不需要插入flash等,还可以加入<object的过滤  
"/(<[^>]*)on[a-za-z]+/s*=([^>]*>)/isu" , //过滤javascript的on事件  
);  
$tarr = array(  
" " ,  
"<//1//2//3>" , //如果要直接清除不安全的标签，这里可以留空  
"//1//2" ,  
);  
$str = preg_replace ( $farr , $tarr , $str );  
return $str; 
}