Bits & Bytes

PHP Cookies, Domains, and Subdomains (oh my!)

Programming in PHP on the web is always interesting, and working with cookies is no exception. For instance, you can set a cookie like this:

setcookie(“a”, “123”);

where “a” is the name and “123” is the value of the cookie.¬† Then you would probably expect it to be available wherever¬† you go in your domain, which we’ll call (Note: do not expect your cookie information to be available if you go to a page on another domain, such as However, what happens when you have a link on your page that takes you to one of your subdomains, like The page in the subdomain needs the cookie you set, but when you arrive at the new page, the cookie is empty. What happened?

Even though crossing from to may not seem like much, it is to a cookie. Cookies are not, by default, available across the subdomains of your domain.

So, when you are on, you can set your cookie with name “a” and value “123” and expect it to be available on any page that has as part of its URL. However, if you want your cookie to be available as well on, or on all of your subdomains and in any of your directories on your domain, you will need to add a few parameters to the call to setcookie(), like this:

setcookie(“a”, “123”, 0, “/”, “”);

  1. “a” is the name of the cookie
  2. “123” is the value of the cookie
  3. 0 is the time of expiration. The default is 0, which means the cookie will expire at the end of the session, which is when the browser closes.
  4. “/” refers to where this cookie works. Setting it to “/” will make it available over the entire domain specified in #5. Otherwise, it will be set for the directory that your script is in, which may not be desired.
  5. “” is the domain over which this cookie remains valid. Adding the “.” to the front of “” will keep the cookie valid over all subdomains of the domain. Do not put “www” in this parameter unless you want the cookie to be valid only over the domain “”. If you do, any page with an “” URL then will not have access to the cookie.

Always remember: you must set a cookie before printing any output to the browser.

This function call will return true if the cookie was successfully set, false otherwise.

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By: Jenna Hall

2 Responses to “PHP Cookies, Domains, and Subdomains (oh my!)”

  1. Om Kumis says:

    I not think this is a best solution for my problem here, coz its still not working with my flow :

    API => curl [create cookie] => redirect [front]

    in middle Im not found the cookie

  2. Aldika says:

    I think performance conncres are unjustified with the technology itself. I had a play with font embedding when it first became available in Firefox (at which point one could assume a large proportion of users could get it and without the evil Microsoft implementation issues).Of course I have the fonts hosted on a folder of my website, so no “google DNS look-up”, no additional CSS fetch (it is in the sites CSS), and I control the cache time on the font files (which can be forever if you serve them with a checksum in the URL), and no complex security headache to ensure Google meant you should be able to snaffle their bandwidth for your sites look and feel.Sure first time a piece of text on the site is rendered in a font there will be a delay, and mobile device users might prefer not to have these in their style sheet. But as long as you don’t go mad and put every piece of text in a different font – it does open up the possibilities.

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