Question

I was working with Guid.NewGuid() in C# , .NET 4.0 . And I’ve found interesting fact: every Guid I’ve generated has ‘4’ at 13 position.

da1471ac-11f7- 4 fb7-a7fa-927fffe8a97c
c90058aa-5d7f- 4 bb5-b3a9-c1db197cf3b1
fa68ec75-8cd2- 4 c24-92f8-41dbbdd428a0
d4efd455-e892- 4 3ef-b7bf-9462c5dc4de4
e0a001a0-8969- 4 092-b7a2-e410ed2b351a
30ae98b9-48ae- 4 25d-b6e7-e091502d6ce2
6a95de82-67ff- 4 4c9-9f7b-e37a80462cf7
66768e46-6d60- 4 2b4-b473-2f6f8bc1559a

I’ve tried it on several machines and have the same result.
Can anybody try it too or explain it?

Simple code for checking:

static void Main(string[] args)
{
     bool ok = false;
     for (int i = 0; i < 10000; i++)
     {
         var guid = Guid.NewGuid();
         if (guid.ToString()[14] != '4')
             ok = true;
         Console.WriteLine(guid);
     }
     Console.WriteLine(ok ? "No bug!" : "4bug founded!");
}

Answer 1

This is indeed the case and not a bug, it’s a feature. It specifies what method was used to generate the GUID. In the case of 4, those GUIDs are generated randomly.

Eric Lippert has a fantastic series on this topic:

Part One
Part Two
Part Three