PHP Manual: Generate a unique ID

Description

string uniqid ([ string $prefix = "" [, bool $more_entropy = false ]] )

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.