rand (PHP 3 <= 3.0.18, PHP 4 >= 4.0.0)rand -- Generate a random value Descriptionint rand (void)int rand (int min, int max) 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). Remember to seed the random number generator before use with srand(). Note: 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(), mt_rand(), mt_srand(), and mt_getrandmax().
(PHP 3 <= 3.0.18, PHP 4 >= 4.0.0)rand -- Generate a random value
Descriptionint rand (void)int rand (int min, int max)
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). Remember to seed the random number generator before use with srand(). Note: 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(), mt_rand(), mt_srand(), and mt_getrandmax().
得到一个32位的字符串
然后只获取它其中的12位就可以了