Hi Guys, just a quick question,

What would be the best way to auto generate a referance number on a contact form which is send to both the owner and customer?

Thanks in advance!

What do you mean by reference number? If you mean what I think you mean then you should try a hash. md5 or sha1

anything you could use to track the contact ?
Like, ddmmyyyy-numeric, or something even totally random, like
http://www.php.net/manual/en/function.uniqid.php

PHP Code:

md5(uniqid(rand(), true)); 


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What is the likelyhood of a collision with uniqueid()? I was thinking just an md5 hash of some of the user's info that is likely to be unique to them:

PHP Code:

$reference = md5($lastName . $firstName . time()); 


Well, uniquId creates an hash based on the epoch time, so the likelyhood is fairly low.
I believe in the order of the micro second. And the rand() with the md5 makes the rest.

As always, there is never enough entropy, and a real random number is almost impossible, but I consider this as a good enough result for what I usually want to do.