Many random number generators of older libcs have
dubious or unknown characteristics and are slow. By default,
PHP uses the libc random number generator with the rand()
function. The mt_rand() function is a
drop-in replacement for this. It uses a random number
generator with known characteristics using the
Mersenne Twister, which will produce random
numbers that should be suitable for seeding some kinds of
cryptography (see the home page for details) and is four
times faster than what the average libc provides.
If called without the optional
min, max arguments
mt_rand() returns a pseudo-random
value between 0 and
RAND_MAX. If you want a random number between 5 and
15 (inclusive), for example, use mt_rand
(5, 15).
In older versions of PHP, you had to seed the random
number generator before use with
mt_srand(). Since 4.2.0 this is no longer
necessary.
注: In versions before 3.0.7 the meaning of max was range. To get the same results in these versions the short example should be mt_rand (5, 11) to get a random number between 5 and 15.
See also mt_srand(),
mt_getrandmax() and rand().