# srand

(PHP 4, PHP 5, PHP 7, PHP 8)

srand — Seed the random number generator

### Descripción

srand(?int `$seed` = `null`, int `$mode` = `MT_RAND_MT19937`): void

Seeds the random number generator with `seed` or with a random value if `seed` is `0`.

> Nota: No es necesario usar una semilla para usar el generador de números aleatorios con srand() o mt_srand() ya que se hace automáticamente.

Precaución

Because the Mt19937 (“Mersenne Twister”) engine accepts only a single 32 bit integer as the seed, the number of possible random sequences is limited to just 232 (i.e. 4,294,967,296), despite Mt19937’s huge period of 219937-1.

When relying on either implicit or explicit random seeding, duplications will appear much earlier. Duplicated seeds are expected with 50% probability after less than 80,000 randomly generated seeds according to the birthday problem. A 10% probability of a duplicated seed happens after randomly generating roughly 30,000 seeds.

This makes Mt19937 unsuitable for applications where duplicated sequences must not happen with more than a negligible probability. If reproducible seeding is required, both the Random\Engine\Xoshiro256StarStar and Random\Engine\PcgOneseq128XslRr64 engines support much larger seeds that are unlikely to collide randomly. If reproducibility is not required, the Random\Engine\Secure engine provides cryptographically secure randomness.

> Nota: As of PHP 7.1.0, srand() has been made an alias of mt_srand().

### Parámetros

`seed`

  Fills the state with values generated with a linear congruential generator that was seeded with `seed` interpreted as an unsigned 32 bit integer.

  If `seed` is omitted or `null`, a random unsigned 32-bit integer will be used.

### Valores devueltos

No devuelve ningún valor.

### Historial de cambios

Versión | Descripción
--- | ---
8.3.0 | `seed` is now nullable.
7.1.0 | srand() has been made an alias of mt_srand().

### Ver también

- rand() - Generate a random integer
- getrandmax() - Show largest possible random value
- mt_srand() - Seeds the Mersenne Twister Random Number Generator