<?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);  } } ?>