1.strip_tags(剥去字符串中的HTML标签)  
strip_tags()函数剥去字符串中的HTML、XML以及PHP的标签。  


2.字符串替换  

str_replace(array(" "," ","\t","\r\n","\r","\n"),array("","","","","","")


3.利用正则表达式(效率稍微低一些)  

$str=preg_replace("/\s+/","",$str);//过滤多余回车  
$str=preg_replace("/<[]+/si","<",$str);//过滤<__("<"号后面带空格)  
$str=preg_replace("/<\!--.*?-->/si","",$str);//注释  
$str=preg_replace("/<(\!.*?)>/si","",$str);//过滤DOCTYPE  
$str=preg_replace("/<(\/?html.*?)>/si","",$str);//过滤html标签  
$str=preg_replace("/<(\/?head.*?)>/si","",$str);//过滤head标签  
$str=preg_replace("/<(\/?meta.*?)>/si","",$str);//过滤meta标签  
$str=preg_replace("/<(\/?body.*?)>/si","",$str);//过滤body标签  
$str=preg_replace("/<(\/?link.*?)>/si","",$str);//过滤link标签  
$str=preg_replace("/<(\/?form.*?)>/si","",$str);//过滤form标签  
$str=preg_replace("/cookie/si","COOKIE",$str);//过滤COOKIE标签  
$str=preg_replace("/<(applet.*?)>(.*?)<(\/applet.*?)>/si","",$str);//过滤applet标签  
$str=preg_replace("/<(\/?applet.*?)>/si","",$str);//过滤applet标签  
$str=preg_replace("/<(style.*?)>(.*?)<(\/style.*?)>/si","",$str);//过滤style标签  
$str=preg_replace("/<(\/?style.*?)>/si","",$str);//过滤style标签  
$str=preg_replace("/<(title.*?)>(.*?)<(\/title.*?)>/si","",$str);//过滤title标签  
$str=preg_replace("/<(\/?title.*?)>/si","",$str);//过滤title标签  
$str=preg_replace("/<(object.*?)>(.*?)<(\/object.*?)>/si","",$str);//过滤object标签  
$str=preg_replace("/<(\/?objec.*?)>/si","",$str);//过滤object标签  
$str=preg_replace("/<(noframes.*?)>(.*?)<(\/noframes.*?)>/si","",$str);//过滤noframes标签  
$str=preg_replace("/<(\/?noframes.*?)>/si","",$str);//过滤noframes标签  
$str=preg_replace("/<(i?frame.*?)>(.*?)<(\/i?frame.*?)>/si","",$str);//过滤frame标签  
$str=preg_replace("/<(\/?i?frame.*?)>/si","",$str);//过滤frame标签  
$str=preg_replace("/<(script.*?)>(.*?)<(\/script.*?)>/si","",$str);//过滤script标签  
$str=preg_replace("/<(\/?script.*?)>/si","",$str);//过滤script标签  
$str=preg_replace("/javascript/si","Javascript",$str);//过滤script标签  
$str=preg_replace("/vbscript/si","Vbscript",$str);//过滤script标签  
$str=preg_replace("/on([a-z]+)\s*=/si","On\\1=",$str);//过滤script标签  
$str=preg_replace("/&#/si","&＃",$str);//过滤script标签，如javAsCript:alert(