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    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.

    See Also

    • 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

    up
    3
    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).
    up
    0
    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
    */
    ?>
    up
    -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.
    up
    -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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