Math Functions
PHP Manual

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
  • mt_getrandmax
  • srand