php下过滤HTML代码的函数

/----------------------
过滤HTML代码的函数
-----------------------/
function htmlEncode($string) {
$string=trim($string);
$string=str_replace("&","&",$string);
$string=str_replace("'","'",$string);
$string=str_replace("&","&",$string);
$string=str_replace(""",""",$string);
$string=str_replace("\"",""",$string);
$string=str_replace("<","<",$string);
$string=str_replace("<","<",$string);
$string=str_replace(">",">",$string);
$string=str_replace(">",">",$string);
$string=str_replace(" "," ",$string);
$string=nl2br($string);
return $string;
}