Is there a way to generate a random number based on a min and max?
For example, if min was 1 and max 20 it should generate any number between 1 and 20, including 1 and 20?
7 Answers
<?php
$min=1;
$max=20;
echo rand($min,$max);
?>
3 Comments
Val
i thought that min and max for rand was the number of digits to use instead of numbers :) thnx
bishop
Related: if
PHP_INT_MAX < ($max-$min), you need to add intervals together, as described in this answer.
xZero
rand() before PHP7.1 is simply bad. It uses LCG algorithm which results with predictable output. It is also slow. Since PHP7.1 rand() is made an alias of mt_rand() therefore no longer bad. PHP7 also introduced cryptographically secure random_int(), however it should be avoided unless essential, since it's much slower than mt_rand()
In a new PHP7 there is a finally a support for a cryptographically secure pseudo-random integers.
int random_int ( int $min , int $max )
random_int — Generates cryptographically secure pseudo-random integers
which basically makes previous answers obsolete.
6 Comments
Matt Cromwell
That's great! But until webhosts support PHP7 more globally, this is not useful for anyone building products for distribution unfortunately. So the previous answers that ALSO work on PHP7 are still best practice.
Uladzimir Pasvistselik
@MattCromwell. I do not agree with you. Until hosting services support PHP7 we should use polyfill for
random_int and random_bytes function - github.com/paragonie/random_compat.
Brian Leishman
I'm curious, is there ever a reason NOT to use
random_int ? If it gives "better" random numbers, why not use it for non-crypto reasons?
Salvador Dali
@BrianLeishman I would rather use it for everything. The only downside that I can guess: it probably relies on the source of randomness and might fail if you are out of randomness. It might be more expensive (need to check) but I doubt that this one function makes a big difference
Brian Leishman
I do know that it's slower, but it's insignificant enough to not go back and change already existing
random_ints to rands. Also, my use case is a retry algorithm, and I definitely don't want multiple failed functions clumping after sleeping because of predictable random ints |
A quicker faster version would use mt_rand:
$min=1;
$max=20;
echo mt_rand($min,$max);
Source: http://www.php.net/manual/en/function.mt-rand.php.
NOTE: Your server needs to have the Math PHP module enabled for this to work. If it doesn't, bug your host to enable it, or you have to use the normal (and slower) rand().
2 Comments
Val
you mean faster right ? the difference is (typing==quicker vs faster==performance wise)
pee2pee
english.stackexchange.com/questions/31732/… - actually can be both
I have bundled the answers here and made it version independent;
function generateRandom($min = 1, $max = 20) {
// Prioritize `random_int` for security
if (function_exists('random_int')) {
return random_int($min, $max); // more secure
}
// Fallback to `mt_rand` if `random_int` isn't available
if (function_exists('mt_rand')) {
return mt_rand($min, $max); // faster
}
// Use `rand` as a last resort.
// Uncomment line below to warn about potential issues
// trigger_error("Using less secure 'rand' function for random number generation. Consider upgrading your PHP version.", E_USER_WARNING);
return rand($min, $max); // old
}
Comments
Comments
rand(1,20)
Docs for PHP's rand function are here:
http://php.net/manual/en/function.rand.php
Use the srand() function to set the random number generator's seed value.
Comments
Try This one. It will generate id according to your wish.
function id()
{
// add limit
$id_length = 20;
// add any character / digit
$alfa = "abcdefghijklmnopqrstuvwxyz1234567890";
$token = "";
for($i = 1; $i < $id_length; $i ++) {
// generate randomly within given character/digits
@$token .= $alfa[rand(1, strlen($alfa))];
}
return $token;
}
random_int(),random_bytes(), oropenssl_random_pseudo_bytes(). as @Salvador Dali saidrand()do not generate cryptographically secure results. See documentation php.net/manual/en/function.rand.php