how to generate unique random numbers in php? - php

Question

I am generating random numbers using php random function, but I want the generated number should be unique and it should not be repeated again.
----------
php code
$number = rand(100,100000); //a six digit random number between 100 to 100000
echo $number;
----------
but I am using this function for multiple times in my code for users so at very rare case there should be a chance of generating same number again. how can i avoid that.

Answer 1

I would do this:
You said you have branches. The receipt id could look something like this:
$dateString = date('Ymd'); //Generate a datestring.
$branchNumber = 101; //Get the branch number somehow.
$receiptNumber = 1; //You will query the last receipt in your database
//and get the last $receiptNumber for that branch and add 1 to it.;
if($receiptNumber < 9999) {
$receiptNumber = $receiptNumber + 1;
}else{
$receiptNumber = 1;
}
Update the receipt database with the receipt number.
$dateString . '-' . $branchNumber . '-' . $receiptNumber;
This will read:
20180406-101-1
This will be unique(Provided you do less than 10,000 transactions a day.) and will show your employees easily readable information.

Answer 2

If you are storing users in DB you should create column [ID] as primary key with auto increment and that would be best solution.
In other case I'd recommend you to simply store all user id's in ascending order from N to M by reading last ID and adding 1 to it because I see no real gain from random order that only adds complexity to your code.

Answer 3

There are many ways, example:
$freq = [];
$number = rand(100,100000);
$times = 10;
while($times-- > 0)
{
while(in_array($number, $freq))$number = rand(100,100000);
$freq[] = $number;
echo $number . "<br>";
}
This will print 10 random unique numbers.

Answer 4

random_int
(PHP 7)
<?php
$number = random_int(100, 100000);
echo $number;

Answer 5

All you need to do is use timestamp in php as timestamp never cross each other hence it will always generate unique number.You can use time() function in php.
The time() function is used to format the timestamp into a human desired format. The timestamp is the number of seconds between the current time and 1st January, 1970 00:00:00 GMT. It is also known as the UNIX timestamp.
<?php
$t=time();
echo $t;
?>
Also you add a rand() function and insert it in front of the $t to make it more random as if few users work at same time then the timestamp might collide.
<?php
$number = rand(100,100000);
$t=time();
$random = $number.''.$t;
echo $random;
?>
The above will reduce the chance to timestamp collide hence making the probability of number uniqueness almost 100%.
And if you make your column unique in your database then the php wont insert the number hence this bottleneck will ensure you will always get a unique random number.
bill_id not null unique

Answer 6

If you are using it for something like user id, then you can use uniqid for that. This command gets a prefixed unique identifier based on the current time in microseconds.
Here's how to use it:
string uniqid ([ string $prefix = "" [, bool $more_entropy = FALSE]] )
Where prefix is used if you are generating ids for a lot if hosts at the same time, you can use this to differentiate between various hosts if id is generated at the same microsecond.
more_entropy increases the likeness of getting unique values.
Usage:
<?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));
?>

Answer 7

this code must work
some description about code:
generate unique id
extract numbers form unique id with regex
gathering numbers from regex with a loop
<?php
$unique = uniqid("",true);
preg_match_all("!\d+!", $unique ,$matches);
print_r($matches);
$numbers = "";
foreach($matches[0] as $key => $num){
$numbers .= $num;
}
echo $numbers;