Random Number Functions in PHP
| Function Name | Function Description |
|---|---|
| getrandmax() | Show largest possible random value |
| mt_getrandmax() | Show largest possible random value |
| mt_rand() | Generate a random value via the Mersenne Twister Random Number Generator |
| mt_srand() | Seeds the Mersenne Twister Random Number Generator |
| rand() | Generate a random integer |
| srand() | Seed the random number generator |
PHP getrandmax() Function
PHP getrandmax() Usage
The PHP getrandmax()rand().
PHP getrandmax() Syntax
getrandmax ( void ) : intPHP getrandmax() Parameters
This function does not accept any parameters.
PHP getrandmax() Return Value
The PHP getrandmax() function returns d by rand()
PHP mt_getrandmax() Function
PHP mt_getrandmax() Usage
The PHP mt_getrandmax()mt_rand().
PHP mt_getrandmax() Syntax
mt_getrandmax ( void ) : intPHP mt_getrandmax() Parameters
This function does not accept any parameters.
PHP mt_getrandmax() Return Value
The PHP mt_getrandmax() function returns the maximum random value returned by a call to mt_rand() without arguments, which is the maximum value that can be used for its max parameter without the result being scaled up (and therefore less random).
PHP mt_getrandmax() Working Examples
1. Calculate a random floating-point number
<?php
function randomFloat($min = 0, $max = 1) {
return $min + mt_rand() / mt_getrandmax() * ($max - $min);
}
var_dump(randomFloat());
var_dump(randomFloat(2, 20));
?>Output of the above code:
float(0.91601131712832)
float(16.511210331931)PHP mt_rand() Function
PHP mt_rand() Usage
The PHP mt_rand()
PHP mt_rand() Syntax
mt_rand ( void ) : int mt_rand ( int $min , int $max ) : intPHP mt_rand() Parameters
min— Optional lowest value to be returned (default: 0)max— Optional highest value to be returned (default:mt_getrandmax())
PHP mt_rand() Return Value
The PHP mt_rand() function returns a random integer value between min (or 0) and max (or mt_getrandmax(), inclusive), or FALSE if max is less than min.
PHP mt_rand() Working Examples
1. mt_rand() example
<?php
echo mt_rand() . "\n";
echo mt_rand() . "\n";
echo mt_rand(5, 15);
?>Output of the above code:
1604716014
1478613278
6Changelog for PHP mt_rand() Function
7.2.0 — mt_rand() has received a bug fix for a modulo bias bug. This means that sequences generated with a specific seed may differ from PHP 7.1 on 64-bit machines.
7.1.0 — rand() has been made an alias of mt_rand().
7.1.0 — mt_rand() has been updated to use the fixed, correct, version of the Mersenne Twister algorithm. To fall back to the old behaviour, use mt_srand() with MT_RAND_PHP as the second parameter.
5.3.4 — Issues an E_WARNING and returns FALSE if max < min.
Important Points about PHP mt_rand() Function
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(), oropenssl_random_pseudo_bytes()instead.minmaxrange must be within the rangemt_getrandmax(). i.e. (max–min) <=mt_getrandmax()Otherwise,mt_rand()may return poorer random numbers than it should.
Additional Tips from Fellow Developers
Contributed By: cyrax21
i wanted to spot out the big difference between rand and mt_rand when producing images using randomness as noise.
for example this is a comparation between rand and mt_rand on a 400x400 pixel png: http://oi43.tinypic.com/vwtppl.jpg
code:
<?php
header("Content-type: image/png");
$sizex=800;
$sizey=400;
$img = imagecreatetruecolor($sizex,$sizey);
$ink = imagecolorallocate($img,255,255,255);
for($i=0;$i<$sizex/2;$i++) {
for($j=0;$j<$sizey;$j++) {
imagesetpixel($img, rand(1,$sizex/2), rand(1,$sizey), $ink);
}
}
for($i=$sizex/2;$i<$sizex;$i++) {
for($j=0;$j<$sizey;$j++) {
imagesetpixel($img, mt_rand($sizex/2,$sizex), mt_rand(1,$sizey), $ink);
}
}
imagepng($img);
imagedestroy($img);
?>
the differences reduce when reducing the pixels of the image.. infact for a 100x100 pixel image the noise produced from the rand function is much more realistic than how it is for a 400x400 image: http://oi39.tinypic.com/5k0row.jpg
(rand is on the left, mt_rand on the right)PHP mt_srand() Function
PHP mt_srand() Usage
The PHP mt_srand()
PHP mt_srand() Syntax
mt_srand ([ int $seed [, int $mode = MT_RAND_MT19937 ]] ) : voidPHP mt_srand() Parameters
seed— An arbitrary integer seed value.mode— Use one of the following constants to specify the implementation of the algorithm to use.
PHP mt_srand() Return Value
The PHP mt_srand() function returns d.
PHP mt_srand() Working Examples
1. mt_srand() example
<?php
// seed with microseconds
function make_seed()
{
list($usec, $sec) = explode(' ', microtime());
return $sec + $usec * 1000000;
}
mt_srand(make_seed());
$randval = mt_rand();
?>Changelog for PHP mt_srand() Function
7.1.0 — srand() has been made an alias of mt_srand().
7.1.0 — mt_rand() has been updated to use the fixed, correct, version of the Mersenne Twister algorithm. To fall back to the old behaviour, use mt_srand() with MT_RAND_PHP as the second parameter.
5.2.1 — The Mersenne Twister implementation in PHP now uses a new seeding algorithm by Richard Wagner. Identical seeds no longer produce the same sequence of values they did in previous versions. This behavior is not expected to change again, but it is considered unsafe to rely upon it nonetheless.
PHP rand() Function
PHP rand() Usage
The PHP rand()getrandmax(). If you want a random number between 5 and 15 (inclusive), for example, use rand(5, 15).
PHP rand() Syntax
rand ( void ) : int rand ( int $min , int $max ) : intPHP rand() Parameters
min— The lowest value to return (default: 0)max— The highest value to return (default:getrandmax())
PHP rand() Return Value
The PHP rand() function returns a pseudo random value between min (or 0) and max (or getrandmax(), inclusive).
PHP rand() Working Examples
1. rand() example
<?php
echo rand() . "\n";
echo rand() . "\n";
echo rand(5, 15);
?>Output of the above code:
7771
22264
11Changelog for PHP rand() Function
7.2.0 — rand() has received a bug fix for a modulo bias bug. This means that sequences generated with a specific seed may differ from PHP 7.1 on 64-bit machines.
7.1.0 — rand() has been made an alias of mt_rand().
Important Points about PHP rand() Function
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(), oropenssl_random_pseudo_bytes()instead.minmaxrange must be within the rangegetrandmax(). i.e. (max-min) <=getrandmax()Otherwise,rand()may return poor-quality random numbers.
Additional Tips from Fellow Developers
Contributed By: Anonymous
quick way to generate randomish numbers and simple strings.
no messing around with functions, so you can just pop the line into the middle of your existing code.
not the most perfect for sure, but ok for plenty of situations...
<?php
$random_number = intval( "0" . rand(1,9) . rand(0,9) . rand(0,9) . rand(0,9) . rand(0,9) ); // random(ish) 5 digit int
$random_string = chr(rand(65,90)) . chr(rand(65,90)) . chr(rand(65,90)) . chr(rand(65,90)) . chr(rand(65,90)); // random(ish) 5 character string
?>
hope someone finds it useful for somthing.
regards,
deeeeeen alxndr0uContributed By: phpdev
Here's an interesting note about the inferiority of the rand() function. Try, for example, the following code...
<?php
$r = array(0,0,0,0,0,0,0,0,0,0,0);
for ($i=0;$i<1000000;$i++) {
$n = rand(0,100000);
if ($n<=10) {
$r[$n]++;
}
}
print_r($r);
?>
which produces something similar to the following output (on my windows box, where RAND_MAX is 32768):
Array
(
[0] => 31
[1] => 0
[2] => 0
[3] => 31
[4] => 0
[5] => 0
[6] => 30
[7] => 0
[8] => 0
[9] => 31
[10] => 0
)
Within this range only multiples of 3 are being selected. Also note that values that are filled are always 30 or 31 (no other values! really!)
Now replace rand() with mt_rand() and see the difference...
Array
(
[0] => 8
[1] => 8
[2] => 14
[3] => 16
[4] => 9
[5] => 11
[6] => 8
[7] => 9
[8] => 7
[9] => 7
[10] => 9
)
Much more randomly distributed!
Conclusion: mt_rand() is not just faster, it is a far superior algorithm.PHP srand() Function
PHP srand() Usage
The PHP srand()seed or with a random value if no seed is given.
PHP srand() Syntax
srand ([ int $seed ] ) : voidPHP srand() Parameters
seed— An arbitrary integer seed value.
PHP srand() Return Value
The PHP srand() function returns d.
PHP srand() Working Examples
1. srand() example
<?php
// seed with microseconds
function make_seed()
{
list($usec, $sec) = explode(' ', microtime());
return $sec + $usec * 1000000;
}
srand(make_seed());
$randval = rand();
?>Changelog for PHP srand() Function
7.1.0 — srand() has been made an alias of mt_srand().
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