Guid.NewGuid Method (System)

I actually think the statement: "The chance that the value of the new Guid will be all zeros or equal to any other Guid is very low.The chance that the value of the new Guid will be all zeros or equal to any other Guid is very low." is very ambiguous.

My understanding is that the NewGuid method on a machine with a Unique MAC address should produce a Guid that is globally unique. Seeing the word "Very Low" is is a bit troubling.

What Is Very Low?

The basic problem is that the global uniqueness of GUIDs across time and space cannot be guaranteed with complete certainty; there is an extremely small possibility of duplication. The documentation uses the phrase "very low". It might have used some other phrase, like "statistically insignificant" or "neglibile" or "virtually non-existent". But neverthless, there is an extremely small probability that duplicate GUIDs can be generated.

--Ron Petrusha
Common Language Runtime User Education
Microsoft Corporation

How can we custom GUID generation of System.Guid.NewGuid() ?
Is there a GuidProvider we can use or program ?

Custom GUID Generation

No, the Guid structure does not support custom GUID generation; you cannot implement a GUID provider that will be called by the static NewGuid method. If you want to add this functionality, you can do it either with an extension method (which will then appear as a static method of the Guid structure, such as Guid.CustomGuid), or with an independent implementation of a GUID that can wrap some of the existing functionality of the Guid structure, such as its parsing and formatting methods.

I hope that this helps to answer your question.

--Ron Petrusha
Common Language Runtime User Education
Microsoft Corporation

NewGuid is a static method, so use the "::" characters in the method call.

PS C:\> [System.Guid]::NewGuid()

Guid
----
7863cacd-a5f1-4941-8c25-8702ab62e799

The GUID object has a GUID property, so to get only that property, type:

PS C:\> [System.Guid]::NewGuid().Guid
7863cacd-a5f1-4941-8c25-8702ab62e799

To get an all-zeros GUID, type:

PS C:\> New-Object System.GUID

Guid
----
00000000-0000-0000-0000-000000000000

Here's a simple function that generates a GUID whenever you need one:

function New-Guid { [System.Guid]::NewGuid().Guid }

To use it, just type "New-Guid".

June Blender
Senior Programming Writer
Windows PowerShell

As part of the GUID originates from the computer hardware, it should not be possible for an all Fs GUID to be created unless the hardware itself was to generate a constant that resulted in all Fs.

Creating a GUID with Specific Digits

It is possible to create a GUID containing all Fs (or any other specified hexadecimal digits, for that matter). The Guid.NewGuid method creates a new GUID with values that depend on the system clock. In contrast, each of the constructors of the GUID structure allow you to create a GUID in which you define all 32 hexadecimal digits of the GUID.

--Ron Petrusha
Common Language Runtime Developer Content
Microsoft Corporation

I am using the all-zeros GUID to represent a "null" GUID, and the all F's GUID to represent the maximum GUID that can be generated.  I've searched on the Internet and it appears that Guid.NewGuid cannot generate the "null" GUID, which is already provided by Guid.Empty; however, what about an all-F's GUID?

An All Fs GUID

I'm not quite sure what your scenario is, but if you need to predictably generate a GUID that contains all Fs, the best way to do it is by calling one of the overloads of the GUID constructor. The best choice is new Guid(new String('F', 32)) (in C#) or New Guid(New String("F"c, 32)) (in Visual Basic).

--Ron Petrusha
CLR Developer Content Team
Microsoft Corporation