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PHP transparently supports HTTP cookies. Cookies are a mechanism for storing data in the remote browser and thus tracking or identifying return users. You can set cookies using the setcookie() or setrawcookie() function. Cookies are part of the HTTP header, so setcookie() must be called before any output is sent to the browser. This is the same limitation that header() has. You can use the output buffering functions to delay the script output until you have decided whether or not to set any cookies or send any headers.
Any cookies sent to you from the client will automatically be included into a $_COOKIE auto-global array if variables_order contains "C". If you wish to assign multiple values to a single cookie, just add  to the cookie name.
Cookies are text files stored on the client computer and they are kept of use tracking purpose. PHP transparently supports HTTP cookies.
There are three steps involved in identifying returning users:
HTTP/1.1 200 OK
Date: Fri, 04 Feb 2000 21:03:38 GMT
Server: Apache/1.3.9 (UNIX) PHP/4.0b3
Set-Cookie: name=xyz; expires=Friday, 04-Feb-07 22:03:38 GMT;
As you can see, the Set-Cookie header contains a name value pair, a GMT date, a path and a domain. The name and value will be URL encoded. The expires field is an instruction to the browser to "forget" the cookie after the given time and date.
If the browser is configured to store cookies, it will then keep this information until the expiry date. If the user points the browser at any page that matches the path and domain of the cookie, it will resend the cookie to the server.The browser's headers might look something like this:
GET / HTTP/1.0
User-Agent: Mozilla/4.6 (X11; I; Linux 2.2.6-15apmac ppc)
Accept: image/gif, */*
A PHP script will then have access to the cookie in the environmental variables $_COOKIE or $HTTP_COOKIE_VARS which holds all cookie names and values. Above cookie can be accessed using $HTTP_COOKIE_VARS["name"].
Setting Cookies with PHP:
PHP provided setcookie() function to set a cookie. This function requires upto six arguments and should be called before tag. For each cookie this function has to be called separately.
setcookie(name, value, expire, path, domain, security);
Here is the detail of all the arguments:
Name - This sets the name of the cookie and is stored in an environment variable called HTTP_COOKIE_VARS. This variable is used while accessing cookies.
Value -This sets the value of the named variable and is the content that you actually want to store.
Expiry - This specify a future time in seconds since 00:00:00 GMT on 1st Jan 1970. After this time cookie will become inaccessible. If this parameter is not set then cookie will automatically expire when the Web Browser is closed.
Path -This specifies the directories for which the cookie is valid. A single forward slash character permits the cookie to be valid for all directories.
Domain - This can be used to specify the domain name in very large domains and must contain at least two periods to be valid. All cookies are only valid for the host and domain which created them.
Security - This can be set to 1 to specify that the cookie should only be sent by secure transmission using HTTPS otherwise set to 0 which mean cookie can be sent by regular HTTP.
Following example will create two cookies name and age these cookies will be expired after one hour.
setcookie("name", "John Watkin", time()+3600, "/","", 0);
setcookie("age", "36", time()+3600, "/", "", 0);
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