///  
     ///  字符截取,中文一个字符两个字节处理
     ///  
     ///  
     ///  
     ///  
     public   static   string  SubString( string  str,  int  length)
    {
        Regex regex  =   new  Regex( " ^[\u4e00-\u9fa5]$ " );

        StringBuilder sb  =   new  StringBuilder();
         int  nLength  =   0 ;

         for  ( int  i  =   0 ; i  <  str.Length; i ++ )
        {
             if  (regex.IsMatch((str[i]).ToString()))
            {
                sb.Append(str[i]);
                nLength  +=   2 ;
            }
             else
            {
                sb.Append(str[i]);
                nLength  =  nLength  +   1 ;
            }
             if  (nLength  >=  length)
                 break ;
        }
         return  sb.ToString();
    }