Generating random numbers

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What is the best way to generating random numbers and you are sure that the
script will never generate the generated ones?



I`m using mysql database, but this out of SQL AUTO_INCREMENT stuff, I need a
real random generator that will never generate what has been generated.

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Re: Generating random numbers

Is the most important thing to be random or to be unique? If you need
unique, you can use a timestamp including microseconds. Maybe using
something like microtime():
http://us.php.net/manual/en/function.microtime.php

The only other way you're probably going to guarentee that you don't repeat
numbers is to keep a list of what's been used and compare against it.
Otherwise, there's always going to be a slim chance you'll repeat a number.

What do you plan on using it for? Maybe someone can give a better
recommendation for what you need. And will this number be generated by
PHP or the database? Or can it be either?

-TG

----- Original Message -----
From: "A. Joseph"
To: "Evert Lammerts"
Cc: "php-db@lists.php.net"
Date: Thu, 17 Apr 2008 00:00:21 +0100
Subject: [PHP-DB] Generating random numbers

> What is the best way to generating random numbers and you are sure that the
> script will never generate the generated ones?
>
> I`m using mysql database, but this out of SQL AUTO_INCREMENT stuff, I need a
> real random generator that will never generate what has been generated.


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Re: Generating random numbers

TG wrote:
> Is the most important thing to be random or to be unique? If you need
> unique, you can use a timestamp including microseconds. Maybe using
> something like microtime():
> http://us.php.net/manual/en/function.microtime.php
>
> The only other way you're probably going to guarentee that you don't repeat
> numbers is to keep a list of what's been used and compare against it.
> Otherwise, there's always going to be a slim chance you'll repeat a number.
>
> What do you plan on using it for? Maybe someone can give a better
> recommendation for what you need. And will this number be generated by
> PHP or the database? Or can it be either?

There's also http://au.php.net/uniqid - you could even use a different
prefix for each call.

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