mt_rand
octdec
Math Functions
PHP Manual

# mt_srand

(PHP 4, PHP 5)

mt_srand — Seed the better random number generator

### Description

void mt_srand ([ int `$seed` ] )

Seeds the random number generator with `seed` or with a random value if no `seed` is given.

> Note: As of PHP 4.2.0, there is no need to seed the random number generator with srand() or mt_srand() as this is now done automatically.

### Parameters

`seed`

  An optional seed value

### Return Values

No value is returned.

### Changelog

Version | Description
--- | ---
4.2.0 | The `seed` becomes optional and defaults to a random value if omitted.
5.2.1 | The Mersenne Twister implementation in PHP now uses a new seeding algorithm by Richard Wagner. Identical seeds no longer produce the same sequence of values they did in previous versions. This behavior is not expected to change again, but it is considered unsafe to rely upon it nonetheless.

### Examples

Example #1 mt_srand() example

`<?php
// seed with microseconds
function make_seed()
{
list($usec, $sec) = explode(' ', microtime());
return (float) $sec + ((float) $usec * 100000);
}
mt_srand(make_seed());
$randval = mt_rand();
?>`

### See Also

- mt_rand() - Generate a better random value
- mt_getrandmax() - Show largest possible random value
- srand() - Seed the random number generator

mt_rand
octdec
Math Functions
PHP Manual