PHP 小方法之 随机生成几位字符串

if(! function_exists ('get_rand_string') ) {
    function get_rand_string($len=6,$format='ALL') {
         switch($format) {
             case 'ALL':
                 $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-@#~'; break;
             case 'CHAR':
                 $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-@#~'; break;
             case 'NUMBER':
                 $chars='0123456789'; break;
             default :
                 $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-@#~';
                 break;
         }
         mt_srand((double)microtime()*1000000*getmypid());
         $password="";
         while(strlen($password)<$len)
            $password.=substr($chars,(mt_rand()%strlen($chars)),1);
         return $password;
     }

}