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Starting a session with session_start()

PHP course · Intermediate · Lesson 82/115

Learn to start a session with session_start() and the session cookie.

What does session_start() do?

HTTP is stateless: each request is independent of the previous one. PHP overcomes this with session_start().

When you call it, PHP sends a session cookie to the browser and opens a separate data area on the server for each user. This area lives in the $_SESSION superglobal.

The cookie carries a unique session id; PHP uses it to find the right data. Call it once at the top of the page, before any output.

The session id and cookie

Every session has a unique identifier: the session id. PHP reads or sets it with session_id(). On the first session_start() call, the id is generated automatically.

The browser stores this id in a cookie named PHPSESSID (default). On later requests the browser sends the cookie back; PHP reads the id and loads the matching $_SESSION data.

You can rename the cookie in php.ini with session.name. The session lives until the cookie expires.

Exercise Print the session status with session_start

Call session_start(). Then, with an if, print active when session_status() equals PHP_SESSION_ACTIVE.

Show example solution 
Call session_start, compare session_status() === PHP_SESSION_ACTIVE in an if, and echo "active".
Example solution:
<?php
// Call session_start and print that the session is active
session_start();
if (session_status() === PHP_SESSION_ACTIVE) {
    echo "active\n";
}

Test yourself

  1. When should session_start() be called?

    • At the very end, after all output
    • Before any output, at the top of the page
    • Only after a database connection
    • On the same line as echo
    Show answer

    Before any output, at the top of the page — Correct. session_start() must be called before output, or you get 'headers already sent'.

  2. Start the session

    <?php
____
$_SESSION = ['counter' => 1];
echo $_SESSION['counter'];
    Show answer 
    <?php
session_start();
$_SESSION = ['counter' => 1];
echo $_SESSION['counter'];

  3. Match the session concepts

    session_start()
    Starts the session
    $_SESSION
    Holds session data
    session_id()
    Returns the session id
    session_destroy()
    Destroys the session

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