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Random string not so random!

Random string not so random!

Random string not so random!


I am working on a system that creates a logical file structure with folders stored in a database. I each folder has a unique identifier. My function to create this is with code I got from the Microsoft website:


Function CreateGUID()
  Randomize Timer
  Dim tmpCounter,tmpGUID
  Const strValid = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  For tmpCounter = 1 To 20
    tmpGUID = tmpGUID & Mid(strValid, Int(Rnd(1) * Len(strValid)) + 1, 1)
  CreateGUID = tmpGUID
End Function 

For some mysterious reason I am getting the occasional folders created with identical GUID values which I would have thought should be extremely unlikely. I also store files in the database with a GUID as well and these also get duplicated from time to time.

Any ideas as to why this might be happening? I thought Randomize Timer was meant to address this sort of issue...

Thanks very much


RE: Random string not so random!

Hi Ed,

From the Microsoft website:


For any given initial seed, the same number sequence is generated because each successive call to the Rnd function uses the previously generated number as a seed for the next number in the sequence.

Before calling Rnd, use the Randomize statement without an argument to initialize the random-number generator with a seed based on the system timer.

I suggest you move the Randomize statement inside the For loop. This way Rnd will return values independent of the previously generated value.

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RE: Random string not so random!

Or use:

CODE -->

Option Explicit

Dim TypeLib, GUID
Set TypeLib = CreateObject("Scriptlet.TypeLib")
GUID = TypeLib.Guid 

RE: Random string not so random!

Thanks guitarzan - really helpful!

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