rand

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

rand — Generate a random integer

Description

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).

Caution

This function does not generate cryptographically secure values, and must not be used for cryptographic purposes, or purposes that require returned values to be unguessable.

If cryptographically secure randomness is required, the Random\Randomizer may be used with the Random\Engine\Secure engine. For simple use cases, the random_int() and random_bytes() functions provide a convenient and secure API that is backed by the operating system’s CSPRNG.

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.

Note: 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().

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
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().

Examples

Example #1 rand() example

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

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

The above example will output something similar to:

7771
22264
11

Notes

Warning

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

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User Contributed Notes 1 note

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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).