rand
(PHP 4, PHP 5)
rand — Generate a random integer
Description
$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
minandmaxwill 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
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.
See Also
- srand() - Seed the random number generator
- getrandmax() - Show largest possible random value
- mt_rand() - Generate a better random value
- openssl_random_pseudo_bytes() - Generate a pseudo-random string of bytes
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Коментарии
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).
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 $d ? chr(rand(65,90)) : chr(rand(48,57)); } echo "\n";'
14BW1A
Note that the algorithm change in version 7.1.0 broke the repeatability of a random sequence initialized with a given value. For example if you have a program like:
<?php
srand($argv[1]);
for ($i = 0; $i < 10; $i++) {
echo rand().PHP_EOL;
}
?>
It will will no longer produce the same results after version 7.1.0. This can be very important for some kinds of simulations. Hopefully you were using mt_rand() or something better all along, otherwise you will have some digging to do if you want your program to be able to repeat simulations from the pre-7.1.0 days... You will need to look in the PHP source archives to discover the algorithm they used to use and replicate it in your program.
Here is a simple base64 random string function
<?php
function random_string($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
*/
?>