Why isn't Guid.ToString(“n”) the same as a hex string generated from a byte array of the same guid?

Question

Consider the following unit test:

    [TestMethod]
    public void TestByteToString()
    {
        var guid = new Guid(\"61772f3ae5de5f4a8577eb1003c5c054\");
           


        

Answer 1

If you compare the results, you can see that the first three groups are reversed:

61 77 2f 3a   e5 de   5f 4a   8577eb1003c5c054
3a 2f 77 61   de e5   4a 5f   8577eb1003c5c054

That's because in the GUID structure, these 3 groups are defined as DWORD and two WORDs rather than bytes:

{0x00000000,0x0000,0x0000,{0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00}}

so in memory, an Intel processor stores them in Little-endian order (the most significant byte the last).

Answer 2

A GUID is structured as follows:

int a
short b
short c
byte[8] d

So for the part represented by a your code gets the bytes reversed. All other parts are transformed correctly.

Answer 3

Well, they are the same, after the first 4 bytes. And the first four are the same, just in the reverse order.

Basically, when created from the string, it's assumed to be in "big-endian" format: Highest byte to the left. However, when stored internally (on an Intel-ish machine), the bytes are ordered "little-endian": highest order byte to the right.