过期cookie - 神奇的数字-86400

Question

I'm reviewing the code of my framework which deletes cookie on client and here is the piece of code where it does it:

return setcookie($name, NULL, -86400, Cookie::$path, Cookie::$domain, Cookie::$secure, Cookie::$httponly);

I'm particularly interested in why the number is -86400 seconds? Is it just random number or it has any special meaning in some convention? I can expire cookie with -1, can't I?

Answer 1

-86400 seconds is exactly a day ago. But that aside, I don't think it has any special meaning. Maybe the guy writing this chose this value to also wipe cookies for browsers that are in a different timezone or of people that have their computer clock set to a slightly incorrect time.

But my guess would be that there used to be 86400 (as a positive number), and the programmer just made it negative to remember the old value, in case they would need it again.