Руководство по PHP
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# uniqid

(PHP 3, PHP 4 , PHP 5)

uniqid -- Generate a unique ID

## Description

string uniqid ( [string prefix [, bool more_entropy]] )

uniqid() returns a prefixed unique identifier based on the current time in microseconds. prefix is optional but can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond. Up until PHP 4.3.1, prefix could only be a maximum of 114 characters long.

If the optional more_entropy parameter is `TRUE`, uniqid() will add additional entropy (using the combined linear congruential generator) at the end of the return value, which should make the results more unique.

With an empty prefix, the returned string will be 13 characters long. If more_entropy is `TRUE`, it will be 23 characters.

> Замечание: The prefix parameter became optional in PHP 5.

If you need a unique identifier or token and you intend to give out that token to the user via the network (i.e. session cookies), it is recommended that you use something along these lines:

`<?php // no prefix $token = md5(uniqid()); // better, difficult to guess $better_token = md5(uniqid(rand(), true)); ?>`

This will create a 32 character identifier (a 128 bit hex number) that is extremely difficult to predict.

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