Generating set of random unique codes in php

Question

I'm trying to generate a set of unique Alpha Numeric code in php. I tried using anonymous function and closures.
Here when I generate more than 1000 codes, there are changes of codes getting duplicate. So I tried to generate a new code if any duplicate found.
Below is my code which isn't working as expected, I'm getting "still DUPLICATE Exist" a few times and its not regenerating code even a single time.

$start = 0;
$count = 10;
$codes = [];
$another = $this;
for ($i=$start; $i < $count; $i++) {
    $getUniqueCode = function (&$codes) use ($another, &$getUniqueCode) {
        $newCode = $another->genRandomCode();
        if (in_array($newCode, $codes)) {
            echo "Regenerate on DUPLICATE FOUND - $newCode <br/>";
            return $getUniqueCode($codes);
        } else {
            return $newCode;
        }
    };
    $newCode = $getUniqueCode($codes);
    if (\in_array($newCode, $codes)) {
        echo "still DUPLICATE Exist - $newCode <br/>";
    }

    array_push($codes, $newCode);
}


private function genRandomCode()
{
    $str = "ABCDEFGHIGKLMNOPQRSTUVWXYZ0123456789";
    $randInt = rand(1000000, 9999999);
    $randString = "";
    for ($i=0; $i < 6; $i++) {
        $randRem = $randInt % 36;
        $randInt = $randInt / 36;
        $randString .= $str[$randRem];
    }
    return $randString;
}

isn't it easier (and safer) to come up with a way for `genRandomCode()` to guarantee a unique value for every call? — Timothy Groote, Aug 04 '17 at 07:56
@RiggsFolly I just wanted it to be either 5 or 6 or fixed digits. — Ankit Balyan, Aug 04 '17 at 08:02
@RiggsFolly that could help, but (of course) it does not guarantee a unique value. (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.) — Timothy Groote, Aug 04 '17 at 08:02
@TimothyGroote `Use more_entropy to increase likelihood of uniqueness. ` — RiggsFolly, Aug 04 '17 at 08:03
I tried `uniqid()` but it generates long string, which isn't required. — Ankit Balyan, Aug 04 '17 at 08:05
https://stackoverflow.com/questions/1846202/php-how-to-generate-a-random-unique-alphanumeric-string — RiggsFolly, Aug 04 '17 at 08:06
Remember if you only have 5 or 6 characters, how many unique version can you expect? How many might you need? — RiggsFolly, Aug 04 '17 at 08:07
I am interested to know what you want these unique id's for? — RiggsFolly, Aug 04 '17 at 08:07
like generating promo / coupon codes, that will appended with 3-4 characters of coupon name. — Ankit Balyan, Aug 04 '17 at 08:08
If I just increase the range, it doesn't generate duplicate, but in case 1% if any duplicate found, I just want to recall to regenerate another one. — Ankit Balyan, Aug 04 '17 at 08:11
People are only going to be impressed with your coupon if it works and gets them a discount. `Coup1`, `Coup2` works for me as long as I get my discount — RiggsFolly, Aug 04 '17 at 08:12
@AnkitBalyan why not generate the codes beforehand, keep track of which ones are used in a database, and select a random unused code every time you need to give out a new coupon? — Timothy Groote, Aug 04 '17 at 08:13
@RiggsFolly people who aren't entitled to a coupon, but can figure out the naming convention will love them too. — Timothy Groote, Aug 04 '17 at 08:13
@TimothyGroote Have you never found a coupon code sharing site??? — RiggsFolly, Aug 04 '17 at 08:14
I'm generating these coupons code to provide it to 3rd party to provide as voucher. Of course it should be some random not in regular fashion. — Ankit Balyan, Aug 04 '17 at 08:15
@RiggsFolly true ;) but you could circumvent that problem by keeping track of the coupon being used, and allow it to be used only once. — Timothy Groote, Aug 04 '17 at 08:15
Its a requirement to generate 100 codes or 1000 at a time for a particular group — Ankit Balyan, Aug 04 '17 at 08:16
@AnkitBalyan this is turning into a large discussion, but generating the possible codes beforehand and picking them out of a queue at random allows you to guarantee unique but nonsequential codes without looping or recursing at the moment you need one of the codes. since you *can* pick out a code from your queue at random, they will not be sequential. — Timothy Groote, Aug 04 '17 at 08:18
@TimothyGroote I've that mechanism for keeping a record of all set used, unused, times a code used and a couple of more.. — Ankit Balyan, Aug 04 '17 at 08:19

Timothy Groote · Accepted Answer · 2017-08-04T08:53:55.530

1

Your original code recurses, but i don't think you need to do that.

$start = 0;
$count = 10;
$codes = [];
$another = $this;
for ($i=$start; $i < $count; $i++) {
    //do not pass $codes as a reference here
    $getUniqueCode = function ($codes) use ($another) 
    {
        $newCode = $another->genRandomCode();
        while(in_array($newCode, $codes))
        {
            echo "Regenerate on DUPLICATE FOUND - $newCode <br/>";
        }

        return $newCode;
    };

    $newCode = $getUniqueCode($codes);
    if (\in_array($newCode, $codes)) {
        echo "still DUPLICATE Exist - $newCode <br/>";
    }

    array_push($codes, $newCode);
}

Arguably however, a better way to handle a coupon system like this is to generate the possible coupon codes beforehand, store them in a database, and select one at random for activation. this guarantees a unique code, and lets you keep track of which codes you have used so far.

edited Aug 04 '17 at 08:53

answered Aug 04 '17 at 08:11

Timothy Groote

8,614
26
52

This is just for generating codes before hands, I've mechanism for keeping a track of used, unused, times a code can be used etc etc. – Ankit Balyan Aug 04 '17 at 08:18
then why not generate them sequentially, and pick a random one that you have not used when you need it? (seems easier. just my $0.02) – Timothy Groote Aug 04 '17 at 08:19
I don't why `in_array($newCode, $codes)` give false always in the inner while loop. but "still DUPLICATE Exist" got printed outside. – Ankit Balyan Aug 04 '17 at 08:30
not even a single time this line "echo "Regenerate on DUPLICATE FOUND - $newCode
";" executes. – Ankit Balyan Aug 04 '17 at 08:31
@AnkitBalyan could the problem be caused by passing `&$codes` (as a reference) into the anonymous function? – Timothy Groote Aug 04 '17 at 08:40
1

I honestly don't know, and i can't run this code myself to check it right now, but try passing it like `$getUniqueCode = function ($codes) use ($another) ` (withouth the ampersand `&` ) – Timothy Groote Aug 04 '17 at 08:40
cool, I tried without `&` in my original code but it didn't work. It works. thanks. :) – Ankit Balyan Aug 04 '17 at 08:49
regarding generating them sequentially, as I wouldn't know how a 3rd party who is distributing code will going to reveal, As I'm just gonna give them all codes at once. – Ankit Balyan Aug 04 '17 at 08:50
@AnkitBalyan well, glad to be of help :) happy coding. – Timothy Groote Aug 04 '17 at 08:53

Generating set of random unique codes in php

1 Answers1