PHP mt_srand() Function

The mt_srand() function seeds the Mersenne Twister random number generator in PHP. The prefix 'mt' stands for Mersenne Twister, which is a high−quality pseudorandom number generator algorithm. While seeding is optional in PHP (done automatically), manual seeding ensures reproducible random sequences or better randomization.

Syntax

mt_srand ([ int $seed [, int $mode = MT_RAND_MT19937 ]] ) : void

Parameters

Return Value

This function does not return any value (void).

Examples

Basic Seeding with Current Time

Using the current timestamp ensures different random sequences each run −

<?php
    mt_srand(time());
    echo "Random number: " . mt_rand();
?>

Random number: 1847236925

Fixed Seed for Reproducible Results

Using a fixed seed generates the same sequence every time −

<?php
    mt_srand(12345);
    echo "First: " . mt_rand() . "<br>";
    echo "Second: " . mt_rand() . "<br>";
    
    // Reset with same seed
    mt_srand(12345);
    echo "Reset First: " . mt_rand() . "<br>";
?>

First: 1914388016
Second: 1289118564
Reset First: 1914388016

Comparing Different Modes

Demonstrating the difference between MT_RAND_MT19937 and MT_RAND_PHP modes −

<?php
    // Using MT19937 mode
    mt_srand(1000, MT_RAND_MT19937);
    echo "MT19937: " . mt_rand() . "<br>";
    
    // Using PHP default mode
    mt_srand(1000, MT_RAND_PHP);
    echo "PHP mode: " . mt_rand();
?>

MT19937: 1244898303
PHP mode: 1244898303

Conclusion

The mt_srand() function provides control over random number generation seeding. Use fixed seeds for reproducible results in testing, or time−based seeds for true randomization in production applications.