little-endian and big-endian

Some computer architectures number bytes in a binary word from left to right, which is referred to as

big-endian. 

Other architectures number the bytes in a binary word from right to left, which is referred to as little-endian.

Using big-endian and little-endian methods, the number 0x12345678 would be stored as shown in the following table.

 

Byte order	Byte 0	Byte 1	Byte 2	Byte 3
Big-endian	0x12	0x34	0x56	0x78
Little-endian	0x78	0x56	0x34	0x12

例子：
下面C# code中有2个txt文件：LittleEndian.txt和BigEndian.txt，他们包含相同的文本内容:都是aa，但不同的编码方式，分别是UCS-2 Little Endian 和UCS-2 Big Endian.

示例中先分别用二进制的方式读出文件中的内容；再用StreamReader读出文件的内容

 static void Main(string[] args)
        {
            byte[] leBytes = ReadAsBinary(".\\LittleEndian.txt");
            Console.WriteLine("Little Endian:");
            PrintByteArray(leBytes);
            Console.WriteLine();

            byte[] bigBytes = ReadAsBinary(".\\BigEndian.txt");
            Console.WriteLine("Big Endian:");
            PrintByteArray(bigBytes);
            Console.WriteLine();

            byte[] srByes;
            using (StreamReader reader = new StreamReader(".\\LittleEndian.txt", true))
            {
                srByes = Encoding.Unicode.GetBytes(reader.ReadToEnd());
            }
            Console.WriteLine("StreamReader Little Endian:");
            PrintByteArray(srByes);
            Console.WriteLine();
}

        private static byte[] ReadAsBinary(string path)
        {
            FileStream fs = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Read);
            BinaryReader breader = new BinaryReader(fs);
            byte[] bytes = breader.ReadBytes(6);
            return bytes;
        }

输出：

结论：

UCS-2 Little Endian编码的文件，其内容以FFFE开头；

UCS-2 Big Endian编码的文件，其内容以FEFF开头；