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unset() and session_destroy()

PHP course · Intermediate · Lesson 85/115

Learn to remove a single session variable with unset() and destroy the whole session with session_destroy().

unset() removes a single variable

To remove a single session variable, use unset($_SESSION['key']). This removes only that key; the rest of the session stays.

For example, to drop one product from a cart, write unset($_SESSION['cart'][$productId]). The whole cart remains.

Note: unset($_SESSION) destroys the whole superglobal but does not close the session. To close it, use session_destroy().

session_destroy() closes the whole session

session_destroy() wipes all session data on the server. The session file is deleted; the next session_start() begins a fresh session.

In a logout flow, first remove the user variable with unset($_SESSION['user']), then close the session with session_destroy().

The cookie may linger in the browser; you can also delete it after session_destroy(). For a basic flow, destroy is enough.

Exercise Remove the cart key and check it

Call session_start(). Set $_SESSION['cart'] = 3. Then remove it with unset($_SESSION['cart']). With if/else, check isset($_SESSION['cart']): if defined print yes, otherwise gone.

Show example solution 
Call session_start, set $_SESSION['cart']=3, call unset($_SESSION['cart']), then if(isset(...)) prints yes/gone.
Example solution:
<?php
// Remove $_SESSION['cart'] with unset and check with isset
session_start();
$_SESSION['cart'] = 3;
unset($_SESSION['cart']);
if (isset($_SESSION['cart'])) {
    echo "yes\n";
} else {
    echo "gone\n";
}

Test yourself

  1. What does session_destroy() do?

    • Removes a single variable
    • Empties $_SESSION but keeps the session open
    • Only deletes the cookie
    • Destroys all session data on the server
    Show answer

    Destroys all session data on the server — Correct. session_destroy() destroys the session data on the server.

  2. Remove a single key

    <?php
session_start();
$_SESSION['cart'] = ['id' => 7, 'qty' => 3];
____
var_dump(isset($_SESSION['cart']));
    Show answer 
    <?php
session_start();
$_SESSION['cart'] = ['id' => 7, 'qty' => 3];
unset($_SESSION['cart']);
var_dump(isset($_SESSION['cart']));

  3. Match the cleanup tools

    unset($_SESSION['k'])
    Removes one key
    session_destroy()
    Destroys the whole session
    session_unset()
    Removes all keys
    session_id()
    Reads the id

All lessons in Intermediate

1 Classes

  1. Defining a class
  2. Defining properties
  3. Defining methods
  4. In-class access with $this
  5. Instantiating with new
  6. Summary - Classes

2 Constructor

  1. The __construct method
  2. Passing parameters to the constructor
  3. Initializing properties
  4. Class type declaration
  5. The __destruct method
  6. Summary - Constructor

3 Inheritance

  1. Inheritance with extends
  2. Accessing parent with parent::
  3. Method override
  4. protected property and method
  5. Inheritance chain
  6. Summary - Inheritance

4 Project: Utility library

  1. Project: Utility library
  2. Class skeleton
  3. Adding methods
  4. Using with file inclusion
  5. Project final - Library

5 Visibility

  1. public access
  2. protected access
  3. private access
  4. Encapsulation
  5. Getter and setter methods
  6. Summary - Visibility

6 Static members

  1. static property
  2. static method
  3. In-class access with self::
  4. Late static binding with static::
  5. static vs instance
  6. Summary - Static members

7 Class constants

  1. Class constants with const
  2. Accessing constants
  3. Class name with ::class
  4. Class constants vs static
  5. Constant use cases
  6. Summary - Class constants

8 Project: Quiz app

  1. Project: Quiz app
  2. Designing a question class
  3. Checking answers
  4. Computing the score
  5. Project final - Quiz app

9 Interfaces

  1. Defining interfaces
  2. Implementing with implements
  3. Multiple interfaces
  4. Polymorphism
  5. interface vs abstract
  6. Summary - Interfaces

10 Abstract classes

  1. Defining abstract classes
  2. abstract methods
  3. Abstract class inheritance
  4. Template method pattern
  5. Constructor and abstract
  6. Summary - Abstract classes

11 Traits

  1. Defining traits
  2. Using traits with use
  3. Multiple traits
  4. Resolving method conflicts
  5. Trait vs inheritance
  6. Summary - Traits

12 Project: Blog app

  1. Project: Blog app
  2. Creating a post class
  3. Adding posts with a form
  4. Displaying the post list
  5. Project final - Blog

13 File handling

  1. Reading with file_get_contents()
  2. Writing with file_put_contents()
  3. Opening files with fopen()
  4. fwrite() and fread()
  5. Closing files with fclose()
  6. Summary - File handling

14 File upload

  1. The $_FILES superglobal
  2. move_uploaded_file()
  3. Validating file type
  4. File size limit
  5. Upload error handling
  6. Summary - File upload

15 Sessions

  1. Starting a session with session_start()
  2. Storing data with $_SESSION
  3. Reading from a session
  4. unset() and session_destroy()
  5. Login/logout logic
  6. Summary - Sessions

16 Cookies

  1. Creating cookies with setcookie()
  2. Reading cookies with $_COOKIE
  3. Cookie expiration
  4. Deleting cookies
  5. Session vs cookie
  6. Summary - Cookies

17 Project: Contact form

  1. Project: Contact form
  2. Form skeleton
  3. Validating data
  4. Integrating file upload
  5. Project final - Contact form

18 Error handling

  1. The try/catch block
  2. Throwing exceptions with throw
  3. The Exception class
  4. error_reporting configuration
  5. Custom exception classes
  6. Summary - Error handling

19 Date and time

  1. Formatting dates with date()
  2. Timestamps with time()
  3. Parsing dates with strtotime()
  4. The DateTime class
  5. DateInterval and DatePeriod
  6. Summary - Date and time

20 Intermediate final

  1. Challenge - OOP app
  2. Challenge - File and session
  3. Challenge - Multi-step registration form
  4. Challenge - Error handling
  5. Challenge - Mini API