<?php
class cls_string_filter{
 //将\n转化为<br/>--囧，这有意思么？
 static public function nl2br($string){
  return nl2br($string);
 }
 //将<br/>转化为\n
 static public function br2nl($string){
  $array = array('<br>','<br/>');
  return str_replace($array,"\n",$string);//字符串替换
 }
 //多个空格只保留一个
 static public function merge_spaces($string){
  return preg_replace("/\s(?=\s)/","\\1",$string);//(?=pattern)举例：abc(?=kk)能匹配abckk，但不能匹配abcdd
 }
 //多个<br/>只保留一个
 static public function merge_brs($string){
  return preg_replace("/((<br\/?>)+)/i","<br>",$string);//---"/"为什么也转义了
 }
 //过滤字符串中的html标签
 static public function strip_tags($string){
  return strip_tags($string);
 }
 //将字符串转换为小写--/--大写
 static public function strtolower($string){
  return strtolower($string);
 }
 static public function strtoupper($string){
  return strtoupper($string);
 }
 //过滤字符串开头与结尾的特定字符
 static public function trim($string,$char_list='\\\\s'){
  $find = array('/[\^\-\]\\\]/S','/\\\{4}/S','/\//');
  $replace = array('\\\\\\0','\\','\/');
  $char = preg_replace($fine,$replace,$char_list);
  $pattern = '^['.$chars.']*|['.$chars.']';
  return preg_replace("/$pattern/sSD",'',$string);
 }
 //过滤字符串中<style>脚本
 static public function stric_style($string){
  $reg = "/<style[^>]*?>.*?<\/style>/is";
  return preg_replace($reg,'',$string);
 }
 //过滤字符串中html危险代码
 static public function strip_html_tags($string){
  $reg = "/(\/?)/(script|iframe|style|html|body|title|meta|\?|\%)([^>]*?>)/is";
  return preg_replace($reg,'',$string);
 }
}
?>