You want to delete a cookie so a browser doesn’t send it back to the server. For example, you’re using cookies to track whether a user is logged in to your website, and a user logs out.
Call setcookie() with no value for the cookie and an expiration time in the past:
It’s a good idea to make the expiration time a long time in the past, in case your server and the user’s computer have unsynchronized clocks.
For example, if your server thinks it’s 3:06 P.M. and a user’s computer thinks it’s 3:02 P.M., a cookie with an expiration time of 3:05 P.M. isn’t deleted by that user’s computer even though the time is in the past for
The call to setcookie() to delete a cookie has to have the same arguments (except for value and time) that the call to setcookie() that set the cookie did, so include the path, domain, and secure flag if necessary.