How to Convert Long to Guid and Vice Versa?

Question

Is this even possible? I don't even think it is, but I saw some code that was trying to do it. However, my unit tests showed that it was not working. I did see some similar thoughts:

• http://stackoverflow.com/questions/401480/converting-guid-to-integer-and-back
• http://stackoverflow.com/questions/3563830/converting-system-decimal-to-system-guid

Just for clarification. The Guid creation is outside of my control; therefore, I can't just store the value in one of the Guid sets.

Answer 1

A GUID is 16 bytes long. A "long" is often understood as being 64 bits (i.e. 8 bytes) long. You cannot convert between those without losing or providing extra data.

Answer 2

You can using Guid constructor, a simple but not flawless example:

Guid g1;
long g2;

// {00000001-0000-0000-0000-000000000000}
g1 = new Guid(1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);

// 00000001
g2 = Convert.ToInt64(g1.ToString().Split('-')[0]);

// 1 + 5 = 6
g2 += 5;

// {00000006-0000-0000-0000-000000000000}
g1 = new Guid((uint)g2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);

The first set can handle up to 4294967295 (int). If you need more than it then you have to use another set.

Each set is a hex representation of a unsigned integer, so you can play around with the possibilities.