C#: 判断txt文件的编码格式

public static Encoding GetTextEncoding(string filePath)
        {
            FileStream fs = new FileStream(filePath, FileMode.Open);
            byte[] buff = new byte[10];
            int result = fs.Read(buff, 0, 10);
            if (result > 3)
            {
                if (buff[0] == 239 && buff[1] == 187 && buff[2] == 191)
                {// utf-8
                    return Encoding.UTF8;
                }
                else if (buff[0] == 254 && buff[1] == 255)
                {// big endian unicode
                    return Encoding.BigEndianUnicode;
                }
                else if (buff[0] == 255 && buff[1] == 254)
                {// unicode
                    return Encoding.Unicode;
                }
                else if (isUtf8(buff))
                {// utf-8
                    return Encoding.UTF8;
                }
                else
                {// ansi
                    return Encoding.Default;
                }
            }
            return null;
        }

        // 110XXXXX, 10XXXXXX
        // 1110XXXX, 10XXXXXX, 10XXXXXX
        // 11110XXX, 10XXXXXX, 10XXXXXX, 10XXXXXX
        private static bool isUtf8(byte[] buff)
        {
            for (int i = 0; i < buff.Length; i++)
            {
                if ((buff[i] & 0xE0) == 0xC0)    // 110x xxxx 10xx xxxx
                {
                    if ((buff[i + 1] & 0x80) != 0x80)
                    {
                        return false;
                    }
                }
                else if ((buff[i] & 0xF0) == 0xE0)  // 1110 xxxx 10xx xxxx 10xx xxxx
                {
                    if ((buff[i + 1] & 0x80) != 0x80 || (buff[i + 2] & 0x80) != 0x80)
                    {
                        return false;
                    }
                }
                else if ((buff[i] & 0xF8) == 0xF0)  // 1111 0xxx 10xx xxxx 10xx xxxx 10xx xxxx
                {
                    if ((buff[i + 1] & 0x80) != 0x80 || (buff[i + 2] & 0x80) != 0x80 || (buff[i + 3] & 0x80) != 0x80)
                    {
                        return false;
                    }
                }
            }
            return true;
        }

参考：

http://blog.csdn.net/xt_chaoji/article/details/7345052

http://blog.csdn.net/nocml/article/details/8106068