Method: Kernel#srand

Defined in:

random.c

#srand(number = Random.new_seed) ⇒ Object

Seeds the system pseudo-random number generator, Random::DEFAULT, with number. The previous seed value is returned.

If number is omitted, seeds the generator using a source of entropy provided by the operating system, if available (/dev/urandom on Unix systems or the RSA cryptographic provider on Windows), which is then combined with the time, the process id, and a sequence number.

srand may be used to ensure repeatable sequences of pseudo-random numbers between different runs of the program. By setting the seed to a known value, programs can be made deterministic during testing.

srand 1234               # => 268519324636777531569100071560086917274
[ rand, rand ]           # => [0.1915194503788923, 0.6221087710398319]
[ rand(10), rand(1000) ] # => [4, 664]
srand 1234               # => 1234
[ rand, rand ]           # => [0.1915194503788923, 0.6221087710398319]

# File 'random.c', line 687

static VALUE
rb_f_srand(int argc, VALUE *argv, VALUE obj)
{
    VALUE seed, old;
    rb_random_t *r = &default_rand;

    if (rb_check_arity(argc, 0, 1) == 0) {
        seed = random_seed(obj);
    }
    else {
	seed = rb_to_int(argv[0]);
    }
    old = r->seed;
    r->seed = rand_init(&r->mt, seed);

    return old;
}