Math Functions
PHP Manual


(PHP 4, PHP 5)

mt_srandSeed the better random number generator


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.



An optional seed value


Version Description
Since 4.2.0 The seed becomes optional and defaults to a random value if omitted.
Since 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.


Example #1 mt_srand() example

// seed with microseconds
function make_seed()
$usec$sec) = explode(' 'microtime());
  return (float) 
$sec + ((float) $usec 100000);
$randval mt_rand();

See Also

Math Functions
PHP Manual