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(gb2312, uft8, temp);

                MessageBox.Show("uft8的编码的字节个数:" + temp1.Length);

                for (int i = 0; i < temp1.Length; i++)

                {

                    MessageBox.Show(Convert.ToUInt16(temp1[i]).ToString());

                }              

                string result = uft8.GetString(temp1);

                return result;

            }

            catch  (Exception ex)//(UnsupportedEncodingException ex)

            {

                MessageBox.Show(ex.ToString());

                return null;

            }

        }

代码说明:

Encoding utf8 = Encoding.GetEncoding(65001);//使用code page

Encoding gb2312 = Encoding.GetEncoding("gb2312");//通过bodyname

获取字符编码字节序列:byte[] temp=utf8.GetBytes(str);

编码方式转换:byte[] temp1=Encoding.Convert(utf8, gb2312, temp);

获取编码的字符串:string str1=gb2312.GetString(temp1);

这样即完成了字符编码的转换。

Encoding.Default在 简体中文os中一般是gb2312格式。