unique id

[cj]

I need to choose a 20 char unique id for transactions handled by my
multithreaded program. I can't decide if to use

Dim uid As String = Guid.NewGuid.ToString
uid = uid.Replace("-", "")
uid = uid.Substring(0, 20)

or

Dim uid as string = Now().Ticks.ToString.PadLeft(20, "0")

 

[Guest]

I need to choose a 20 char unique id for transactions handled by my
multithreaded program. I can't decide if to use

Dim uid As String = Guid.NewGuid.ToString
uid = uid.Replace("-", "")
uid = uid.Substring(0, 20)

You don't need to do the replace line - the .ToString command has
different formatters:

http://msdn2.microsoft.com/en-us/library/system.guid.tostring.aspx

and in particular:

http://msdn2.microsoft.com/en-us/library/97af8hh4.aspx

Guid.NewGuid.ToString("N") will return an all numeric value.

Also you can't take a substring of a GUID and expect it to be unique...
A GUID is only unique if all 32 digits are present.

or

Dim uid as string = Now().Ticks.ToString.PadLeft(20, "0")

While the resolution of ticks is quite good, I'm not sure this can
gaurantee uniqueness as well. It really depends on how many concurrent
requests you're planning on handling.

Take a look at this:

http://www.codinghorror.com/blog/archives/000409.html

Shows you how to convert a 16byte GUID into a 20 byte ASCII
representation

 

[cj]

Dim uid As String = Guid.NewGuid.ToString("N")
MessageBox.Show(uid)

returns letters too.

 

[Guest]

Dim uid As String = Guid.NewGuid.ToString("N")
MessageBox.Show(uid)

returns letters too.

There should be no dashes however.

 

[cj]

Correct.

I've discussed it here and since we've been using the first 20 of guid
I'm going to continue with that bad tradition. I can't count on ticks
to be unique either after all and I need max 20 and I don't feel like
working with another component like ASCII85.

Thanks for you help.

 

[Guest]

Correct.

I've discussed it here and since we've been using the first 20 of guid
I'm going to continue with that bad tradition. I can't count on ticks
to be unique either after all and I need max 20 and I don't feel like
working with another component like ASCII85.

You shoudl just an incrementing counter ;-)

 

[Chris Dunaway]

I've discussed it here and since we've been using the first 20 of guid
I'm going to continue with that bad tradition. I can't count on ticks
to be unique either after all and I need max 20 and I don't feel like
working with another component like ASCII85.

You can't count on the first 20 characters of a guid to be unique
either. Why can't you use the entire guid? That you can count on to
be unique.

 

[cj]

Field I'm putting it in is 20 chars.

Like I said however if they've been getting by with the first 20 chars
in the past I'll just continue the bad practice.