/* 
* 中文截取，支持gb2312,big5 
* @param 
* @author 编程之家 jb51.cc jb51.cc
* @param string $str 要截取的字串 
* @param int $start 截取起始位置 
* @param int $length 截取长度 
* @param string $charset utf-8|gb2312|gbk|big5 编码 
* @param $suffix 是否加尾缀 
*/ 
public function csubstr($str,$start=0,$length,$charset="utf-8",$suffix=true) 
{ 
if(function_exists("mb_substr")) 
{ 
if(mb_strlen($str,$charset) <= $length) return $str; 
$slice = mb_substr($str,$start,$charset); 
} 
else 
{ 
$re['utf-8'] = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|[\xe0-\xef][\x80-\xbf]{2}|[\xf0-\xff][\x80-\xbf]{3}/"; 
$re['gb2312'] = "/[\x01-\x7f]|[\xb0-\xf7][\xa0-\xfe]/"; 
$re['gbk'] = "/[\x01-\x7f]|[\x81-\xfe][\x40-\xfe]/"; 
$re['big5'] = "/[\x01-\x7f]|[\x81-\xfe]([\x40-\x7e]|\xa1-\xfe])/"; 
preg_match_all($re[$charset],$str,$match); 
if(count($match[0]) <= $length) return $str; 
$slice = join("",array_slice($match[0],$length)); 
} 
if($suffix) return $slice."…"; 
return $slice; 
}