Well, that really depends on how the input comes in. But if you need to validate whether a string is a UUID, there are a couple of ways to do that.

First is by trying to convert the string to a UUID and catching the error.

 private bool IsValidGUID(string GUIDCheck)
  {
   bool retVal = false;
   try  to convert the string to a guid
   {
    Guid g = new Guid(GUIDCheck);
     We successfully converted it, return true
    retVal = true;
   }
   catch (System.FormatException)   The string was not in a GUID format
   { retVal = false; }
   catch (Exception ex)  Something else went wrong, let the caller figure it out
   { throw ex;  }
   return retVal;
  }

The downside to this is that throwing errors can be expensive. A better version is to RegEx it (original source, Andrew Gunn), simplified here:

private bool IsValidGUID(string GUIDCheck)
  {
   if (!string.IsNullOrEmpty(GUIDCheck))
   {
    return new Regex(@"^(\{{0,1}([0-9a-fA-F]){8}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){12}\}{0,1})$").IsMatch(GUIDCheck);
   }
   return false;
  }

Note: My only change is not using a variable.

So, how much faster is it? A simple test that processed 50 valid and 50 invalid UUIDs 100 times showed the following times:

• RegEx Average to process 50 valid/50 invalid UUIDs:     5.85 ms
• Catch Average to process 50 valid/50 invalid UUIDs: 493.17 ms

That's not even including the memory costs involved in using a Catch nor the aborted threads.

That's today's lesson, RegEx is better.

Josef

PS... Source for the test available if you want it.