mt_srand(): Seeds the Mersenne Twister Random Number Generator
Seed mt_rand() only when reproducibility is intentional
PHP normally seeds the Mersenne Twister automatically. Call mt_srand() only when you intentionally need a repeatable pseudo-random sequence, such as a controlled demonstration; it is not a security mechanism.
mt_srand(1234);
echo mt_rand(1, 100);
Manual time-based seeding is unnecessary because PHP seeds the generator automatically.
Syntaxvoid mt_srand(?int $seed = null, int $mode = MT_RAND_MT19937)
| Parameter | DESCRIPTION |
|---|---|
| $seed | Optional : Seed used |
| $mode | Optional: use MT_RAND_MT19937. The legacy MT_RAND_PHP mode is deprecated as of PHP 8.3. |
Automatic seeding is normally sufficient
Do not call mt_srand(time()) for normal random generation. PHP already initializes the global generator automatically.
Example 2: Using a Fixed Seed for Reproducibility
<?php
mt_srand(123);
echo mt_rand(); // Same seed starts the same pseudo-random sequence for the same algorithm/version
?>
Example 3: Generating a Sequence of Random Numbers with a Seed
<?php
mt_srand(42);
for($i = 0; $i < 5; $i++) {
echo mt_rand() . "<br>";
}
?>
Example 4: Resetting the Seed with Different Values
<?php
mt_srand(100);
echo mt_rand(); // Output: A specific pseudo-random number
mt_srand(200);
echo mt_rand(); // Output: A different specific pseudo-random number
?>
Example 5: Repeatable demonstration data
<?php
mt_srand(7);
$lottery_numbers = [];
for($i = 0; $i < 6; $i++) {
$lottery_numbers[] = mt_rand(1, 49);
}
echo implode(", ", $lottery_numbers); // Repeatable demonstration values; not suitable for a real lottery
?>
Math Functions mt_rand(): Mersenne Twister integers random_int(): secure random integers
Subhendu Mohapatra
Author & Instructor at plus2net
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