The code is valid, assuming that the variable $imgD
is defined [var_dump
is one way of checking this, but print
or echo
may also work].
Check to ensure that cookies are enable in your browser.
Also, be sure that session_start[] comes near the top of your script, it should be the first thing sent to the client each time.
To test a session, create "index.php" with the following code:
Reload the page several times and you should see an incrementing number.
An example of passing session variables between two pages is as follows:
PageOne.php
PageTwo.php
For simplicity put PageOne.php and PageTwo.php in the same directory. Call PageOne.php and then PageTwo.php.
Try also tutorials here, here, and here.
A session is a way to store information [in variables] to be used across multiple pages.
Unlike a cookie, the information is not stored on the users computer.
What is a PHP Session?
When you work with an application, you open it, do some changes, and then you close it. This is much like a Session. The computer knows who you are. It knows when you start the application and when you end. But on the internet there is one problem: the web server does not know who you are or what you do, because the HTTP address doesn't maintain state.
Session variables solve this problem by storing user information to be used across multiple pages [e.g. username, favorite color, etc]. By default, session variables last until the user closes the browser.
So; Session variables hold information about one single user, and are available to all pages in one application.
Tip: If you need a permanent storage, you may want to store the data in a database.
Start a PHP Session
A session is started with the session_start[]
function.
Session variables are set with the PHP global variable: $_SESSION.
Now, let's create a new page called "demo_session1.php". In this page, we start a new PHP session and set some session variables:
Example
Run example »
Note: The session_start[]
function must be the very first thing in your document. Before any HTML tags.
Get PHP Session Variable Values
Next, we create another page called "demo_session2.php". From this page, we will access the session information we set on the first page ["demo_session1.php"].
Notice that session variables are not passed individually to each new page, instead they are retrieved from the session we open at the beginning of each page [session_start[]
].
Also notice that all session variable values are stored in the global $_SESSION variable:
Example
Run example »
Another way to show all the session variable values for a user session is to run the following code:
Example
Run example »
How does it work? How does it know it's me?
Most sessions set a user-key on the user's computer that looks something like this: 765487cf34ert8dede5a562e4f3a7e12. Then, when a session is opened on another page, it scans the computer for a user-key. If there is a match, it accesses that session, if not, it starts a new session.
Modify a PHP Session Variable
To change a session variable, just overwrite it:
Example
Run example »
Destroy a PHP Session
To remove all global session variables and destroy the session, use session_unset[]
and session_destroy[]
:
Example
Run example »