❮ PHP Misc Reference
Definition and Usage
The uniqid[] function generates a unique ID based on the microtime [the current time in microseconds].
Note: The generated ID from this function does not guarantee uniqueness of the return value! To generate an extremely difficult to predict ID, use the md5[] function.
Syntax
uniqid[prefix,more_entropy]
Parameter Values
| prefix | Optional. Specifies a prefix to the unique ID [useful if two scripts generate ids at exactly the same microsecond] |
| more_entropy | Optional. Specifies more entropy at the end of the return value. This will make the result more unique. When set to TRUE, the return string will be 23 characters. Default is FALSE, and the return string will be 13 characters long |
Technical Details
| Returns the unique identifier, as a string |
| 4+ |
| The prefix parameter became optional in PHP 5.0. The limit of 114 characters long for prefix was raised in PHP 4.3.1. |
❮ PHP Misc Reference
[PHP 4, PHP 5, PHP 7, PHP 8]
uniqid — Generate a unique ID
Description
uniqid[string $prefix = "", bool $more_entropy = false]: string
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
prefixCan 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