utf-8转gb2312 的问题

public string convertStr(string str)

    {



        Encoding utf8 = Encoding.UTF8;

        Encoding gb2312 = Encoding.GetEncoding(936);



        byte[] utf8Bytes = utf8.GetBytes(str);



        byte[] gb2312Bytes = Encoding.Convert(utf8, gb2312, utf8Bytes);



        char[] gb2312Chars = new char[gb2312.GetCharCount(gb2312Bytes, 0, gb2312Bytes.Length)];

        gb2312.GetChars(gb2312Bytes, 0, gb2312Bytes.Length, gb2312Chars, 0);

        string gb2312Str = new string(gb2312Chars);



        return gb2312Str;

    }