#27683 [Opn->Csd]: rand() and mt_rand() require seeding

ID: 27683 Updated by: derick@php.net Reported By: x13 at rpgsource dot net -Status: Open +Status: Closed Bug Type: Math related Operating System: Windows 2000 Professional (SP3) PHP Version: 4.3.4 New Comment: This bug has been fixed in CVS. Snapshots of the sources are packaged every three hours; this change will be in the next snapshot. You can grab the snapshot at http://snaps.php.net/. Thank you for the report, and for helping us make PHP better. Previous Comments: ------------------------------------------------------------------------ [2004-03-24 18:08:52] x13 at rpgsource dot net Description: ------------ Hello, I run a script using the command-line interface which generates three random numbers and writes them, along with the date, to a logfile. Using timers on the mIRC chat program, I run this script every 45 seconds: dos SILENT C:\apache\php\php.exe D:\htdocs\private\sites\fake\fake.php The "dos SILENT" command simply opens cmd.exe in the background and executes whatever parameters I pass. It's equivalent to: C:\>C:\apache\php\php.exe D:\htdocs\private\sites\fake\fake.php I have many other applications (including other PHP scripts) running in this manner. I am 99.9% sure the way I execute php.exe (with "dos SILENT") has nothing to do with this problem. I run Apache/1.3.29 (Win32) with a basically-standard httpd.conf file and PHP 4.3.4 with an unedited php.ini file. At first, using rand(), the random numbers were being generated just fine. I checked the logfile a while later and noticed that identical random numbers were being chosen and logged: 03/23/04, 23:10:21 (8, 1, 358) 03/23/04, 23:11:02 (8, 1, 358) 03/23/04, 23:11:55 (8, 1, 358) 03/23/04, 23:12:36 (8, 1, 358) I tried switching to mt_rand(); the problem persisted. I then tried seeding the random number generator once, using the example provided in the manual, and it began working correctly: 03/24/04, 07:36:33 (8, 1, 634) 03/24/04, 07:37:18 (8, 0, 680) 03/24/04, 07:38:03 (4, 0, 677) 03/24/04, 07:38:48 (4, 0, 10) I found nothing mentioned in the bug database or in the user comments for rand()'s manual section. I'd be willing to experiment further, if necessary; just contact me. Thank you. Reproduce code: --------------- <?php function make_seed() { list($usec, $sec) = explode(' ', microtime()); return (float) $sec + ((float) $usec * 100000); } mt_srand(make_seed()); $rand = array(mt_rand(1,9), mt_rand(0,1), mt_rand(1,700)); $log_p = fopen("log.txt", "a"); fwrite($log_p, date("m/d/y, H:i:s")." ($rand[0], $rand[1], $rand[2])\n"); fclose($log_p); ?> Expected result: ---------------- I expected three random numbers to be generated and written to log.txt, such as: 03/24/04, 07:36:33 (8, 1, 634) 03/24/04, 07:37:18 (8, 0, 680) 03/24/04, 07:38:03 (4, 0, 677) 03/24/04, 07:38:48 (4, 0, 10) Actual result: -------------- Without the code: function make_seed() { list($usec, $sec) = explode(' ', microtime()); return (float) $sec + ((float) $usec * 100000); } mt_srand(make_seed()); ...my results were: 03/23/04, 23:10:21 (8, 1, 358) 03/23/04, 23:11:02 (8, 1, 358) 03/23/04, 23:11:55 (8, 1, 358) 03/23/04, 23:12:36 (8, 1, 358) ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=27683&edit=1