How to Start Session in PHP: Simple Guide with Examples

To start a session in PHP, use the session_start() function at the very beginning of your script before any output. This function initializes a session or resumes the current one, allowing you to store and access user data across pages.

Syntax

The basic syntax to start a session in PHP is simple:

• session_start(); - This function must be called before any HTML or output is sent to the browser.

It initializes a new session or resumes an existing one, enabling you to use the $_SESSION superglobal array to store user data.

php

<?php
session_start();
?>

Example

This example shows how to start a session, store a value, and then access it on the same page.

php

<?php
session_start();

// Store data in session
$_SESSION['username'] = 'Alice';

// Access and display session data
echo 'Hello, ' . $_SESSION['username'] . '!';
?>

Output

Hello, Alice!

Common Pitfalls

Common mistakes when starting sessions include:

• Calling session_start() after outputting HTML or whitespace, which causes errors.
• Not calling session_start() on every page where session data is accessed.
• Forgetting to check if session variables exist before using them.

php

<?php
// Wrong: output before session_start()
echo 'Welcome!';
session_start(); // Causes error

// Right: session_start() first
session_start();
echo 'Welcome!';
?>

Quick Reference

Remember these tips when working with PHP sessions:

• Always call session_start() at the very top of your script.
• Use $_SESSION to store and retrieve session data.
• Sessions help keep user data across multiple pages.

Key Takeaways

Always call session_start() before any output to start or resume a session.

Use the $_SESSION array to store and access user data across pages.

Call session_start() on every page where you want to use session data.

Avoid sending any output before session_start() to prevent errors.

Check if session variables exist before using them to avoid warnings.