round

rad2deg

[edit] Last updated: Fri, 15 Mar 2013

view this page in

rand

(PHP 4, PHP 5)

rand — Generate a random integer

Description

int rand ( void )

int rand ( int $min , int $max )

If called without the optional min, max arguments rand() returns a pseudo-random integer between 0 and getrandmax(). If you want a random number between 5 and 15 (inclusive), for example, use rand(5, 15).

Note: On some platforms (such as Windows), getrandmax() is only 32767. If you require a range larger than 32767, specifying min and max will allow you to create a range larger than this, or consider using mt_rand() instead.

Parameters

min: The lowest value to return (default: 0)
max: The highest value to return (default: getrandmax())

Return Values

A pseudo random value between min (or 0) and max (or getrandmax(), inclusive).

Changelog

Version	Description
4.2.0	The random number generator is seeded automatically.

Examples

Example #1 rand() example


<?php
echo rand() . "\n";
echo rand() . "\n";

echo rand(5, 15);
?>

The above example will output something similar to:

7771
22264
11

Notes

Caution

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 openssl_random_pseudo_bytes() instead.


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.

down

matheus at matheusloureiro dot com ¶

1 month ago


If you are looking for generate a random expression, like password with alphanumeric or any other character, use this function:





<?php


function GeraHash($qtd){


//Under the string $Caracteres you write all the characters you want to be used to randomly generate the code.


$Caracteres = 'ABCDEFGHIJKLMOPQRSTUVXWYZ0123456789';


$QuantidadeCaracteres = strlen($Caracteres);


$QuantidadeCaracteres--;





$Hash=NULL;


    for($x=1;$x<=$qtd;$x++){


        $Posicao = rand(0,$QuantidadeCaracteres);


        $Hash .= substr($Caracteres,$Posicao,1);


    }





return $Hash;


}





//Here you specify how many characters the returning string must have


echo GeraHash(30);


?>

down

Zak ¶

1 year ago


I couldn't find a suitable random alpha-numeric generator function so I rolled my own. It gives a random number in base 36 (0-9, a-z) to a given length.





<?php


function randomAlphaNum($length){





    $rangeMin = pow(36, $length-1); //smallest number to give length digits in base 36


    $rangeMax = pow(36, $length)-1; //largest number to give length digits in base 36


    $base10Rand = mt_rand($rangeMin, $rangeMax); //get the random number


    $newRand = base_convert($base10Rand, 10, 36); //convert it


    


    return $newRand; //spit it out





}


?>





hopefully helps someone

down

relsqui at armory dot com ¶

8 years ago


Don't forget, it's faster to use bitwise operations when you need a random number that's less than some power of two. For example,



<?php

rand()&1;

// instead of

rand(0,1);

// for generating 0 or 1,



rand()&3;

// instead of

rand(0,3);

// for generating 0, 1, 2, or 3,



rand()&7;

// instead of

rand(0,7)

// for generating 0, 1, 2, 3, 4, 5, 6, or 7,

?>



and so on. All you're doing there is generating a default random number (so PHP doesn't have to parse any arguments) and chopping off the piece that's useful to you (using a bitwise operation which is faster than even basic math).

down

david [at] ddrewdesign [dot] com ¶

3 years ago


To Jano and Peta:



Thanks for the code. In real world usage, I only had one problem with it: It will never return the first result of the array (or it will return nothing if there's only one item in the array). To remedy this, I simply subtracted 1 from 



<?php

$rand = rand(1,$max);

?>



like so:



<?php

$rand = rand(1,$max)-1;

?>



Thanks though, for the code you supplied. It was exactly what I needed.

down

kyle dot florence [@t] gmail dot com ¶

3 years ago


Improved random string generation function:



<?php

// Generate a random character string

function rand_str($length = 32, $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890')

{

    // Length of character list

    $chars_length = (strlen($chars) - 1);



    // Start our string

    $string = $chars{rand(0, $chars_length)};

    

    // Generate random string

    for ($i = 1; $i < $length; $i = strlen($string))

    {

        // Grab a random character from our list

        $r = $chars{rand(0, $chars_length)};

        

        // Make sure the same two characters don't appear next to each other

        if ($r != $string{$i - 1}) $string .=  $r;

    }

    

    // Return the string

    return $string;

}

?>

down

Alex Khimch alex at khim dot removeit dot ich dot org ¶

1 year ago


Random is NOT actually random.



It is easily illustrated by multiplying rand(1,500) by rand(1,500) and showing the output on the image:



<?php

header("Content-type: image/png");

$img = imagecreatetruecolor(500,500);



$ink = imagecolorallocate($img,255,255,255);



for($i=0;$i<500;$i++) {

  for($j=0;$j<500;$j++) {

  imagesetpixel($img, rand(1,500), rand(1,500), $ink1);

  }

}



imagepng($img);

imagedestroy($img);



?>



I expected to get pixel noise, but instead one can see plain diagonal lines.

down

liveonaware [at] gmail [dot] com ¶

2 years ago


<?php

//To Pull 7 Unique Random Values Out Of AlphaNumeric



//removed number 0, capital o, number 1 and small L

//Total: keys = 32, elements = 33

$characters = array(

"A","B","C","D","E","F","G","H","J","K","L","M",

"N","P","Q","R","S","T","U","V","W","X","Y","Z",

"1","2","3","4","5","6","7","8","9");



//make an "empty container" or array for our keys

$keys = array();



//first count of $keys is empty so "1", remaining count is 1-6 = total 7 times

while(count($keys) < 7) {

    //"0" because we use this to FIND ARRAY KEYS which has a 0 value

    //"-1" because were only concerned of number of keys which is 32 not 33

    //count($characters) = 33

    $x = mt_rand(0, count($characters)-1);

    if(!in_array($x, $keys)) {

       $keys[] = $x;

    }

}



foreach($keys as $key){

   $random_chars .= $characters[$key];

}

echo $random_chars;

?>

down

Justin Richer ¶

11 months ago


Since many people (myself included) come to this page looking for a way to do a random string, I present a way that uses arrays and shuffle() instead of rand(). This also has the effect of not repeating any characters in the value set.



    $arr = str_split('ABCDEFGHIJKLMNOP'); // get all the characters into an array

    shuffle($arr); // randomize the array

    $arr = array_slice($arr, 0, 6); // get the first six (random) characters out

    $str = implode('', $arr); // smush them back into a string

down

John Galt ¶

3 years ago


Another way to create an array of random numbers where there are no identical numbers.



($n = number of random numbers to return in the array

$min = minimum number

$max = maximum number)



<?php

 function uniqueRand($n, $min = 0, $max = null)

 {

  if($max === null)

   $max = getrandmax();

  $array = range($min, $max);

  $return = array();

  $keys = array_rand($array, $n);

  foreach($keys as $key)

   $return[] = $array

rand

Description

Parameters

Return Values

Changelog

Examples

Notes

See Also