php下过滤html代码的函数 提高程序安全性

function ihtmlspecialchars($string) {
if(is_array($string)) {
foreach($string as $key => $val) {
$string[$key] = ihtmlspecialchars($val);
}
} else {
$string = preg_replace('/&((#(\d{3,5}|x[a-fA-F0-9]{4})|[a-zA-Z][a-z0-9]{2,5});)/', '&\\1',
str_replace(array('&', '"', '<', '>'), array('&amp;', '&quot;', '&lt;', '&gt;'), $string));
}
return $string;
}

function htmlEncode($string) {
$string=trim($string);
$string=str_replace("&","&",$string);
$string=str_replace("'","'",$string);
$string=str_replace("&amp;","&",$string);
$string=str_replace("&quot;",""",$string);
$string=str_replace("\"",""",$string);
$string=str_replace("&lt;","<",$string);
$string=str_replace("<","<",$string);
$string=str_replace("&gt;",">",$string);
$string=str_replace(">",">",$string);
$string=str_replace("&nbsp;"," ",$string);
$string=nl2br($string);
return $string;
}