# uniqid

(PHP 4, PHP 5, PHP 7)

uniqid — Generate a unique ID

### Description

uniqid ([ string `$prefix` = "" [, bool `$more_entropy` = `FALSE` ]] ) : string

Gets a prefixed unique identifier based on the current time in microseconds.

Caution

This function does not generate cryptographically secure values, and should not be used for cryptographic purposes. If you need a cryptographically secure value, consider using random_int(), random_bytes(), or openssl_random_pseudo_bytes() instead.

Warning

This function does not guarantee uniqueness of return value. Since most systems adjust system clock by NTP or like, system time is changed constantly. Therefore, it is possible that this function does not return unique ID for the process/thread. Use `more_entropy` to increase likelihood of uniqueness.

### Parameters

`prefix`

  Can be useful, for instance, if you generate identifiers simultaneously on several hosts that might happen to generate the identifier at the same microsecond.

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

`more_entropy`

  If set to `TRUE`, uniqid() will add additional entropy (using the combined linear congruential generator) at the end of the return value, which increases the likelihood that the result will be unique.

### Return Values

Returns timestamp based unique identifier as a string.

Warning

This function tries to create unique identifier, but it does not guarantee 100% uniqueness of return value.

### Examples

Example #1 uniqid() Example

`<?php
/* A uniqid, like: 4b3403665fea6 */
printf("uniqid(): %s\r\n", uniqid());
/* We can also prefix the uniqid, this the same as
* doing:
*
* $uniqid = $prefix . uniqid();
* $uniqid = uniqid($prefix);
*/
printf("uniqid('php_'): %s\r\n", uniqid('php_'));
/* We can also activate the more_entropy parameter, which is
* required on some systems, like Cygwin. This makes uniqid()
* produce a value like: 4b340550242239.64159797
*/
printf("uniqid('', true): %s\r\n", uniqid('', true));
?>`

### Notes

> Note:

> Under Cygwin, the `more_entropy` must be set to `TRUE` for this function to work.