uniqid
(PHP 4, PHP 5)
uniqid — Generate a unique ID
Description
$prefix = ""
[, bool $more_entropy = false
]] )Gets a prefixed unique identifier based on the current time in microseconds.
This function does not create random nor unpredictable strings. This function must not be used for security purposes. Use a cryptographically secure random function/generator and cryptographically secure hash functions to create unpredictable secure IDs.
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. Ifmore_entropyisTRUE, 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 the unique identifier, as a string.
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));
?>
Changelog
| Version | Description |
|---|---|
| 5.0.0 |
The prefix parameter was made optional.
|
| 4.3.1 |
The limit of 114 characters long for prefix
was raised.
|
Notes
This function does not generate cryptographically secure tokens, in fact without being passed any additional parameters the return value is little different from microtime(). If you need to generate cryptographically secure tokens use openssl_random_pseudo_bytes().
Note:
Under Cygwin, the
more_entropymust be set toTRUEfor this function to work.
Коментарии
Just to note this function is fairly slow, and can bring your script to a crawl if it is in a loop. Strangely if you run it as uniqid('', true) it runs much more quickly