题外话：关于C#读取文件编码那些事，能不改写一段代码进quicker呀。

static void Main()
{
    PrintText("gb2312.txt");
    PrintText("unicode.txt");
}

//根据文件自动觉察编码并输出内容
static void PrintText(string path)
{
    var enc = GetEncoding(path, Encoding.GetEncoding("GB2312"));
    using (var sr = new StreamReader(path, enc))
    {
        Console.WriteLine(sr.ReadToEnd());
    }
}

/// <summary>
/// 根据文件尝试返回字符编码
/// </summary>
/// <param name="file">文件路径</param>
/// <param name="defEnc">没有BOM返回的默认编码</param>
/// <returns>如果文件无法读取，返回null。否则，返回根据BOM判断的编码或者缺省编码（没有BOM）。</returns>
static Encoding GetEncoding(string file, Encoding defEnc)
{
    using (var stream = File.OpenRead(file))
    {
        //判断流可读？
        if (!stream.CanRead)
            return null;
        //字节数组存储BOM
        var bom = new byte[4];
        //实际读入的长度
        int readc;

        readc = stream.Read(bom, 0, 4);

        if (readc >= 2)
        {
            if (readc >= 4)
            {
                //UTF32，Big-Endian
                if (CheckBytes(bom, 4, 0x00, 0x00, 0xFE, 0xFF))
                    return new UTF32Encoding(true, true);
                //UTF32，Little-Endian
                if (CheckBytes(bom, 4, 0xFF, 0xFE, 0x00, 0x00))
                    return new UTF32Encoding(false, true);
            }
            //UTF8
            if (readc >= 3 && CheckBytes(bom, 3, 0xEF, 0xBB, 0xBF))
                return new UTF8Encoding(true);

            //UTF16，Big-Endian
            if (CheckBytes(bom, 2, 0xFE, 0xFF))
                return new UnicodeEncoding(true, true);
            //UTF16，Little-Endian
            if (CheckBytes(bom, 2, 0xFF, 0xFE))
                return new UnicodeEncoding(false, true);
        }

        return defEnc;
    }
}

//辅助函数，判断字节中的值
static bool CheckBytes(byte[] bytes, int count, params int[] values)
{
    for (int i = 0; i < count; i++)
        if (bytes[i] != values[i])
            return false;
    return true;
}