If called without the optional
min, max arguments
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 rand (5, 15).
In older versions of PHP, you had to seed the random
number generator before use with 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 rand (5, 11) to get a random number between 5 and 15.
See also srand(),
getrandmax(), and mt_rand().