php生成随机数或者字符串的代码

代码如下：

/** 
* 产生随机字符串 
* 
* 产生一个指定长度的随机字符串,并返回给用户 
* 
* @access public 
* @param int $len 产生字符串的位数 
* @return string 
*/ 
function randstr($len=6) { 
$chars='ABCDEFGHIJKLMNOPQRSTUVWXYZ 
abcdefghijklmnopqrstuvwxyz0123456789-@#~'; 
// characters to build the password from 
mt_srand((double)microtime()*1000000*getmypid()); 
// seed the random number generater (must be done) 
$password=''; 
while(strlen($password)<$len) 
$password.=substr($chars,(mt_rand()%strlen($chars)),1); 
return $password; 
}