(PHP 4, PHP 5, PHP 7)
uniqid — Generate a unique ID
$prefix= "" [, bool
$more_entropy= false ]] )
Gets a prefixed unique identifier based on the current time in microseconds.
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.
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
increase likelihood of uniqueness.
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
TRUE, it will be 23 characters.
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.
Returns timestamp based unique identifier as a string.
This function tries to create unique identifier, but it does not guarantee 100% uniqueness of return value.
Example #1 uniqid() Example
/* A uniqid, like: 4b3403665fea6 */
printf("uniqid(): %s\r\n", uniqid());
/* We can also prefix the uniqid, this the same as
* $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));
Under Cygwin, the
more_entropymust be set to
TRUEfor this function to work.