php 截取中文字符

<?php
/*
*截取字符串
*bilibo@2011-06-23
*/

class StringHelper extends AppHelper {
	
	function CutStr($string, $sublen, $start = 0, $code = 'UTF-8') {
    
    
    if($code == 'UTF-8') {
    	
    	$pa = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/";
    	preg_match_all($pa, $string, $t_string);
    	
    	if( count( $t_string[0] ) - $start > $sublen ) {
    		
    		return join('', array_slice($t_string[0], $start, $sublen));
    		
    	}
    	
    	return join('', array_slice($t_string[0], $start, $sublen));
    	
    } else {
    	
    	$start = $start * 2;
    	$sublen = $sublen * 2;
    	$strlen = strlen($string);
    	$tmpstr = '';
    	
    	for($i=0; $i<$strlen; $i++) {
    		
    		if($i>=$start && $i<($start+$sublen)) {
    			
    			if(ord(substr($string, $i, 1))>129) $tmpstr.= substr($string, $i, 2);
    			
    			else $tmpstr.= substr($string, $i, 1);
    		}
    		
    		if( ord( substr($string, $i, 1 ) ) > 129 ) $i++;
    		
     }
     
     if( strlen($tmpstr) < $strlen )
     
     return $tmpstr;
     
     }
  
  }
}
?>