No matter if you decide to for

$_SESSION['UniqueRandomTemporaryID'] = 'h0ss5qul55mpev38uaduca31c0';
# or
$_COOKIE['UniqueRandomTemporaryID'] = 'h0ss5qul55mpev38uaduca31c0';

it will set a cookie this way or another.

Cookies are sent by the server to the browser and only the domain that ordered the cookie to be set is allowed to read it. So far the theory.



only difference is, that with session_start(); the only way to modify the „session-timeout“ is possible via php.ini.

if i search the firefox-home-profile-directory i find:

# looking for PHP_SESSION_ID cookie in firefox-profile folder
find . -type f | xargs grep -s -l "h0ss5qul55mpev38uaduca31c0"

# found it here

so the PHP-$_SESSION is basically automatic-php-session-id-cookies.

while with custom-cookies, you can/have to generate your own session-id and also specify how long the cookie is valid etc. pp.

maybe like that:

/* generate as random as possible 16-character string */
function salt()
// generate a 16-character salt string
$salt = substr(str_replace('+','_',base64_encode(md5(mt_rand(), true))),0,16);
$salt = str_replace('/','_',$salt);
$salt = str_replace('\','_',$salt);
return $salt;

Alternatives? Yes, but…

you could append the sessionID to the url… and keep it passing around…

Otherwise, you can set your session.use_only_cookies to „0“ to force the appendage of a session ID to URLs within your php. This approach, however, has several draw backs. Mainly that of keeping the state within the URL, as opposed to the Cookie header. If a user were to copy and paste the URL of the page they were on, and someone else were to click on it, they would both be using the same session.


     ini_set("session.use_cookies", 0);
     ini_set("session.use_only_cookies", 0);
     ini_set("session.use_trans_sid", 1);
     ini_set("session.cache_limiter", "");



(PHP 4, PHP 5, PHP 7)

setcookieSend a cookie


setcookie() defines a cookie to be sent along with the rest of the HTTP headers. Like other headers, cookies must be sent before any output from your script (this is a protocol restriction). This requires that you place calls to this function prior to any output, including <html> and <head> tags as well as any whitespace.

Once the cookies have been set, they can be accessed on the next page load with the $_COOKIE array. Cookie values may also exist in $_REQUEST.


» RFC 6265 provides the normative reference on how each setcookie() parameter is interpreted.


The name of the cookie.


The value of the cookie. This value is stored on the clients computer; do not store sensitive information. Assuming the


is ‚cookiename‘, this value is retrieved through $_COOKIE[‚cookiename‘]


The time the cookie expires. This is a Unix timestamp so is in number of seconds since the epoch. In other words, you’ll most likely set this with the time() function plus the number of seconds before you want it to expire. Or you might use mktime(). time()+60*60*24*30 will set the cookie to expire in 30 days. If set to 0, or omitted, the cookie will expire at the end of the session (when the browser closes).


You may notice the


parameter takes on a Unix timestamp, as opposed to the date format Wdy, DD-Mon-YYYY HH:MM:SS GMT, this is because PHP does this conversion internally.


The path on the server in which the cookie will be available on. If set to ‚/‘, the cookie will be available within the entire


. If set to ‚/foo/‘, the cookie will only be available within the /foo/ directory and all sub-directories such as /foo/bar/ of


. The default value is the current directory that the cookie is being set in.


The (sub)domain that the cookie is available to. Setting this to a subdomain (such as ‚‘) will make the cookie available to that subdomain and all other sub-domains of it (i.e. To make the cookie available to the whole domain (including all subdomains of it), simply set the value to the domain name (‚‘, in this case).

Older browsers still implementing the deprecated » RFC 2109 may require a leading . to match all subdomains.


Indicates that the cookie should only be transmitted over a secure HTTPS connection from the client. When set to


, the cookie will only be set if a secure connection exists. On the server-side, it’s on the programmer to send this kind of cookie only on secure connection (e.g. with respect to $_SERVER[„HTTPS“]).




the cookie will be made accessible only through the HTTP protocol. This means that the cookie won’t be accessible by scripting languages, such as JavaScript. It has been suggested that this setting can effectively help to reduce identity theft through XSS attacks (although it is not supported by all browsers), but that claim is often disputed. Added in PHP 5.2.0.




Return Values

If output exists prior to calling this function, setcookie() will fail and return


. If setcookie() successfully runs, it will return


. This does not indicate whether the user accepted the cookie.


Some examples follow how to send cookies:

Example #1 setcookie() send example

$value = 'something from somewhere';
setcookie("TestCookie", $value);
setcookie("TestCookie", $value, time()+3600);  /* expire in 1 hour */
setcookie("TestCookie", $value, time()+3600, "/~rasmus/", "", 1);

Note that the value portion of the cookie will automatically be urlencoded when you send the cookie, and when it is received, it is automatically decoded and assigned to a variable by the same name as the cookie name. If you don’t want this, you can use setrawcookie() instead if you are using PHP 5. To see the contents of our test cookie in a script, simply use one of the following examples:

// Print an individual cookie
echo $_COOKIE["TestCookie"];
// Another way to debug/test is to view all cookies

Example #2 setcookie() delete example

When deleting a cookie you should assure that the expiration date is in the past, to trigger the removal mechanism in your browser. Examples follow how to delete cookies sent in previous example:

// set the expiration date to one hour ago
setcookie("TestCookie", "", time() - 3600);
setcookie("TestCookie", "", time() - 3600, "/~rasmus/", "", 1);

Example #3 setcookie() and arrays

You may also set array cookies by using array notation in the cookie name. This has the effect of setting as many cookies as you have array elements, but when the cookie is received by your script, the values are all placed in an array with the cookie’s name:


// set the cookies
setcookie("cookie[three]", "cookiethree");
setcookie("cookie[two]", "cookietwo");
setcookie("cookie[one]", "cookieone");
// after the page reloads, print them out
if (isset($_COOKIE['cookie'])) {
foreach ($_COOKIE['cookie'] as $name => $value) {
$name = htmlspecialchars($name);
$value = htmlspecialchars($value);
echo "$name : $value <br />\n";

The above example will output:

three : cookiethree
two : cookietwo
one : cookieone


Version Description
5.5.0 A Max-Age attribute is now included in the Set-Cookie header sent to the client.
5.2.0 The


parameter was added.



You can use output buffering to send output prior to the call of this function, with the overhead of all of your output to the browser being buffered in the server until you send it. You can do this by calling ob_start() and ob_end_flush() in your script, or setting the output_buffering configuration directive on in your php.ini or server configuration files.


If the PHP directive register_globals is set to on then cookie values will also be made into variables. In our examples below, $TestCookie will exist. It’s recommended to use $_COOKIE.

Common Pitfalls:

  • Cookies will not become visible until the next loading of a page that the cookie should be visible for. To test if a cookie was successfully set, check for the cookie on a next loading page before the cookie expires. Expire time is set via the

    parameter. A nice way to debug the existence of cookies is by simply calling print_r($_COOKIE);.

  • Cookies must be deleted with the same parameters as they were set with. If the value argument is an empty string, or

    , and all other arguments match a previous call to setcookie, then the cookie with the specified name will be deleted from the remote client. This is internally achieved by setting value to ‚deleted‘ and expiration time to one year in past.

  • Because setting a cookie with a value of

    will try to delete the cookie, you should not use boolean values. Instead, use 0 for


    and 1 for



  • Cookies names can be set as array names and will be available to your PHP scripts as arrays but separate cookies are stored on the user’s system. Consider explode() to set one cookie with multiple names and values. It is not recommended to use serialize() for this purpose, because it can result in security holes.

Multiple calls to setcookie() are performed in the order called.