public string UTF8ToGB2312(string str)

        {

            try

            {    

                Encoding utf8 = Encoding.GetEncoding(65001);

                Encoding gb2312 = Encoding.GetEncoding("gb2312");//Encoding.Default ,936

                byte[] temp = utf8.GetBytes(str);

                byte[] temp1 = Encoding.Convert(utf8, gb2312, temp);

                string result = gb2312.GetString(temp1); 

                return result;

            }

            catch  (Exception ex)//(UnsupportedEncodingException ex)

            {

                MessageBox.Show(ex.ToString());

                return null; 

            }

        }

        public string GB2312ToUTF8(string str)

        {

            try

            {

                Encoding uft8 = Encoding.GetEncoding(65001);

                Encoding gb2312 = Encoding.GetEncoding("gb2312");

                byte[] temp = gb2312.GetBytes(str);

                MessageBox.Show("gb2312的编码的字节个数：" + temp.Length);

                for (int i = 0; i < temp.Length; i++)

                {

                    MessageBox.Show(Convert.ToUInt16(temp[i]).ToString());

                }    

                byte[] temp1 = Encoding.Convert