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Reading from a session

PHP course · Intermediate · Lesson 84/115

Learn to read data from $_SESSION and check existence with isset().

Reading data from $_SESSION

You read session data with $_SESSION['key']. But if the key is missing, PHP raises a warning. To avoid this, check existence with isset().

If isset($_SESSION['lang']) returns true, the key is defined and safe to read. If false, it is undefined; use a default value.

Tip: $_SESSION['lang'] ?? 'en' (null coalescing) gives you both the check and a default in one line.

Defaults for missing keys

When reading from a session, a key may be undefined. Two common approaches: an if/else with isset(), or the null coalescing operator ??.

$lang = isset($_SESSION['lang']) ? $_SESSION['lang'] : 'en'; is the classic ternary form. Shorter: $lang = $_SESSION['lang'] ?? 'en';

Both do the same: if undefined, return 'en'; otherwise the stored value. The short form is preferred in modern PHP 8.

Exercise Read a default language from a missing key

Call session_start(). With if/else, check isset($_SESSION['lang']): if defined, assign the stored value to $lang; otherwise assign 'en'. Then echo $lang.

Show example solution 
Call session_start, use if(isset($_SESSION['lang'])) to set $lang from the session, else 'en', then echo $lang.
Example solution:
<?php
// Print the default language if $_SESSION['lang'] is missing
session_start();
if (isset($_SESSION['lang'])) {
    $lang = $_SESSION['lang'];
} else {
    $lang = 'en';
}
echo $lang . "\n";

Test yourself

  1. Complete the isset key check

    <?php
session_start();
$_SESSION['count'] = 5;
if (____ && $_SESSION['count'] > 0) {
    echo 'ok';
} else {
    echo 'en';
}
    Show answer 
    <?php
session_start();
$_SESSION['count'] = 5;
if (isset($_SESSION['lang']) && $_SESSION['count'] > 0) {
    echo 'ok';
} else {
    echo 'en';
}

  2. What does isset($_SESSION['missing']) return?

    • true
    • 1
    • false
    • null
    Show answer

    false — Correct. When the key is undefined, isset returns false.

  3. Match the session reading tools

    isset($_SESSION['k'])
    Checks if key exists
    $_SESSION['k']
    Reads the value
    ?? 'default'
    Gives default if undefined
    empty()
    Checks if empty

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