how to generate unique id in php based on current data and time?

Question

I need to generate a unique ID in php based on current date and time to keep a log of when i am running code. i.e. every time i run the code it should be able to generate a unique id based on current date and time.

Hope I am clear with my ques. How to do that?

Christiachristian

use time stamp, its always unique – Vegetative

codepad.org/LGM4MjX2 , timestamps – Vegetative

@Vegetative are you sure there won't be any conflict if i run the code any number of times and any day? – Christiachristian

check answer, add mt_rand() if you need to make sure about random values, time should do the work too. – Vegetative

Oh my God... How can Unix timestamps with a 1-second resolution be unique? – Loquitur

why you guys think the time stamp won't be unique (not saying you are wrong), so same time in a timezone will never come again ,so a unix time stamp for that time is generated only once, right? – Vegetative

@Vegetative Call same function 5 times in 0.0002s. Unix timestamp will be the same, as it's same second. Also run 2 processes at exact same time (e.g. 2 parallel requests) - timestamp is for all processes. You are very wrong. – Iatrochemistry

@Vegetative Same your example, just with more calls: codepad.org/Isj2lCnd – Iatrochemistry

agreed, I was so wrong! – Vegetative

Answer 1

Using time() to create sortable unique id's

Concatenating strings will also further randomize your desired result and still keep it sortable. manual here

$uniqueId= time().'-'.mt_rand();

Vegetative

Answer 2

With PHP 7 you can use this to generate a sufficiently random value based on the current timestamp:

$s = time() . bin2hex(random_bytes(10));

Do note that after 265 years (starting with 11 digits in 2286) the timestamp would get another digit, and sorting order will be off; if your code is expected to survive for that long, you may want to consider some padding.

Old answer

You can use a combination of uniqid() and time() like so:

$s = uniqid(time(), true);

Example output:

1346136883503c6b3330caf5.19553126

Fathometer

We can also complexify the generation of a unique id with the function md5 md5(uniqid(time(), true)). – Eijkman

"does not guarantee uniquenes" ; "Use more_entropy to increase likelihood of uniqueness". So it's not really unique, but the conflict will be less probable. – Endive

Answer 3

Is this what you're looking for? uniqid()

From the doc:

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

Eweneck

will it generate uniqueid() based on time only?? if so what happens if there is a time conflict...i am not clear.. i need a manual code that generates unique id every time i run the code @Mythril – Christiachristian

You'll possibly get the same ID if your IDs are generated on the same microsecond. It's difficult but could happen. You can make it harder by appending a random string--the base technique is good IMHO. – Loquitur

php.net/manual/en/function.uniqid.php the doc indicates that you can provide a prefix and an entropy source. – Eweneck

what do they mean by prefix string? I dont get it.. entropy too.. @Mythril – Christiachristian

A prefix is an arbitrary string that you provide to give the id extra meaning/differentiate it (it's up to you really). An entropy source is just an additional number (preferably random or pseudo-random) that will make the id less likely to collide with previously generated ids. – Eweneck

have you tried 'time().'-'.mt_rand();'.. can you ensure uniqid() gives a better result than this? i mean what is the best way.. no offence. – Christiachristian

do you want to store Id's in sorted order? – Vegetative