PHP Chinese character interception function_PHP tutorial

public function substrgb($in,$num)
    {
      //$num=16;
      $pos=0;
      $bytenum=0;
      $out="";
      while($num){
    
    $c=mb_substr($in,$pos,1,"euc-jp");
    if($c=="n") break;
    if(strlen($c)==1){
      $pos++;
      $bytenum++;
      if($bytenum>$num) break;
      $out.=$c;                        
    }
    else
      {
        $pos++;
        $bytenum=$bytenum+2;
        if($bytenum>$num) break;
        $out.=$c;                   
      }
      }
      return $out;
    }