rand

(PHP 4, PHP 5, PHP 7, PHP 8)

rand — Generate a random integer

Descrizione

rand(): int

rand(int $min, int $max): int

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).

Attenzione

Questa funzione non genera valori crittograficamente sicuri, e non dovrebbe essere usata per scopi di crittografia. Se c'è necessità di utilizzare un valore crittograficamente sicuro, si preferisca openssl_random_pseudo_bytes().

Nota: 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.

Nota: As of PHP 7.1.0, rand() uses the same random number generator as mt_rand(). To preserve backwards compatibility rand() allows max to be smaller than min as opposed to returning false as mt_rand().

Elenco dei parametri

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

Valori restituiti

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

Log delle modifiche

Versione	Descrizione
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().

Esempi

Example #1 rand() example

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

echo rand(5, 15), "\n";
?>

Il precedente esempio visualizzerà qualcosa simile a:

7771
22264
11

Note

Avviso

min max range must be within the range getrandmax(). i.e. (max - min) <= getrandmax() Otherwise, rand() may return poor-quality random numbers.

Vedere anche:

srand() - Seed the random number generator
getrandmax() - Show largest possible random value
mt_rand() - Generate a random value via the Mersenne Twister Random Number Generator
random_int() - Get a cryptographically secure, uniformly selected integer
random_bytes() - Get cryptographically secure random bytes

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User Contributed Notes 4 notes

down

relsqui at armory dot com ¶

19 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

play dot it at play-it dot net ¶

1 year ago


Here is a simple base64 random string function

<?php
function random_string($length) {
    $str = random_bytes($length);
    $str = base64_encode($str);
    $str = str_replace(["+", "/", "="], "", $str);
    $str = substr($str, 0, $length);
    return $str;
}

/*
Example outputs for random_string(32)

OP0vOJEsSvr6wbgN4jIwqMMstlpMSUsl
2IHaIxD2W4VTKZuzioudbpQCALdl6Ym6
QY0eZ3QYy3OKKN6ttzbDwAwsAfkXfQ2f
jznjlPCUDbYzOTJysPP414BbdVNu4jmT
GlktgJ8JUhdH5MfQ1PHl0wnqXQlKggQs
Pb9WALM3KcGCCPBKXsPgNfy3M0Xj4aEu
AED6OTVl8aBbspdxoXvA1sT4ein8lruH
9cSbz4FhoI4qSsPZFMh0u1rWDDEgQxI2
iSBlT4K7Ad516qPXgPReSj2tii7TAK5b
DuX8HByMb2e8IdM4j49Td2JTI9Ki7o1C
*/
?>

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-5

Anonymous ¶

4 years ago


Note that the algorithm change in version 7.1.0 broke the repeatability of a random sequence initialized with a given value. For example if you have a program like:

<?php
srand($argv[1]);
for ($i = 0; $i < 10; $i++) {
    echo rand().PHP_EOL;
}
?>

It will will no longer produce the same results after version 7.1.0. This can be very important for some kinds of simulations. Hopefully you were using mt_rand() or something better all along, otherwise you will have some digging to do if you want your program to be able to repeat simulations from the pre-7.1.0 days... You will need to look in the PHP source archives to discover the algorithm they used to use and replicate it in your program.

down

-11

Anonymous ¶

14 years ago


Generate a random 5 character A-Z0-9  string



<?php

for ($i=0; $i<6; $i++) { 

    $d=rand(1,30)%2; 

    echo $d ? chr(rand(65,90)) : chr(rand(48,57)); 

}

?>



# php -r 'for ($i=0; $i<6; $i++) { $d=rand(1,30)%2; echo $d ? chr(rand(65,90)) : chr(rand(48,57)); } echo "\n";'

14BW1A

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