Oops, 36^8 :)
This value would only have to generated perhaps a few times an hour, but
should't take more than a second to compute. These values ARE being stored
in a database; however, once this database gets to a million or so rows, it
would take a very long time to check it doesn't overlap, wont it?
I also thought about getting the current date/time stamp and representing it
as this value. This code is an online-order reference number, so it could be
something like seconds since midnight:
36^4 = 1,679,616
Seconds in a day (60.60.24) = 86400
A really effective way would be to get a subsecond count for the day; so
that 0000 is midnight, and ZZZZ is the end of the that day. This means there
are about 19 increments a second, which rules out any possibility of
duplicates, because:
1. two other characters could be the id of the user (a numeric value). 36.36
is 33696, which is much higher than the intended number of users on the
system (we invisage no more than a few hundred - by the time the userbase
gets to 33000, I'll be a millionairre and this can be someone else's job
hehe)
2. the two remaining characters could be a day/year thing. perhaps the days
since the start of the year 2000. 33696/365 is 92; this system will not be
used for 92 years!
Does that sound like quite a good algorythm, or do you have a much easier,
simpler way?
Siggy
----- Original Message -----
From: "Larry Forrister" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, January 24, 2001 7:26 AM
Subject: Re: [PHP-WIN] Random Code
> Do you mean W3E4-22ER would be valid? If so there would be 36^8
> (2,821,109,907,456) possible values.
>
> A truly random generator algorithm cannot guarantee uniqueness. I'm
> guessing what you want is to generate each possible value once in a
> pseudo-random order. Would just apparent randomness suffice?
>
> With what frequency do the values need to be generated? Once every few
> seconds/minutes or multiple times per second?
> ~~LF
>
>
> Sigurd Magnusson wrote:
>
> > Whats the best way to make a completely random, unique code in the
> > format "ABCD-1234" where each of the 8 characters can be alphanumerc;
> > 0-9,A-Z... I thought about generating a 36^4 number, converting to to
> > base '36', and repeating the process. What's a good way to ensure the
> > code is not repeated, though?
> >
> > Siggy
>
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