Tag: Lesson 9: PHP Sessions and Cookies

In this lesson, we will explore how to manage state in PHP using cookies and sessions. These tools allow you to store data about users and their interactions with your website, providing the foundation for features like user authentication, shopping carts, and preferences.

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9.1 Setting and Retrieving Cookies

What are Cookies?

• Definition: Small pieces of data stored on the client’s browser.
• Purpose: Track user activity, preferences, or login sessions.
• Lifetime: Cookies can persist for a set duration or until the browser is closed.

Setting Cookies

Use the setcookie() function to create cookies.

• Syntax:
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  setcookie(name, value, expire, path, domain, secure, httponly);

  • name: Name of the cookie.
  • value: Value to be stored.
  • expire: Expiration time in UNIX timestamp format.
  • path: Path where the cookie is accessible.
  • domain: Domain where the cookie is valid.
  • secure: Whether to transmit over HTTPS only.
  • httponly: Restrict cookie access to HTTP(S) protocols only.

Example: Setting a Cookie

Retrieving Cookies

Access cookies using the $_COOKIE superglobal.

Example: Deleting a Cookie

• Set the expiration time to a past date.

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9.2 Working with Sessions

What are Sessions?

• Definition: Sessions store data on the server for a user during their visit.
• Purpose: Keep track of user data across multiple pages (e.g., shopping cart, login state).
• Lifetime: Active until the user closes the browser or the session times out.

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Starting a Session

• Use the session_start() function at the beginning of your script to initialize a session.
• Syntax:
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  session_start();


Storing Session Data

• Store data in the $_SESSION superglobal array.

Accessing Session Data

• Access session variables using the $_SESSION array.

Destroying a Session

• Use session_unset() to clear session variables and session_destroy() to terminate the session.

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Comparison of Cookies and Sessions

Feature	Cookies	Sessions
Storage	Client-side	Server-side
Security	Less secure (stored in the browser)	More secure (stored on the server)
Data Size	Limited (4KB per cookie)	Unlimited (depends on server memory)
Lifetime	Can persist after browser is closed	Ends when browser is closed or timed out
Use Cases	Remember user preferences or login state	Shopping carts, user authentication

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Practical Examples

Example 1: Login System with Sessions

1. Login Form:
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   <form method="POST" action="login.php">
Username: <input type="text" name="username"><br>
<input type="submit" value="Login">
</form>

2. Processing Login:
   php

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   <?php
session_start();
if ($_SERVER["REQUEST_METHOD"] == "POST") {
$_SESSION["username"] = $_POST["username"];
echo "Welcome, " . $_SESSION["username"];
}
?>

3. Displaying User Data:
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   <?php
session_start();
if (isset($_SESSION["username"])) {
echo "Hello, " . $_SESSION["username"];
} else {
echo "Please log in.";
}
?>

4. Logout:
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   <?php
session_start();
session_unset();
session_destroy();
echo "You have logged out.";
?>


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Example 2: Remember Me with Cookies

1. Login Form:
   php

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   <form method="POST" action="remember_me.php">
Username: <input type="text" name="username"><br>
<input type="checkbox" name="remember" value="1"> Remember Me<br>
<input type="submit" value="Login">
</form>

2. Processing Login:
   php

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   <?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
$username = $_POST["username"];
if (isset($_POST["remember"])) {
setcookie("username", $username, time() + 3600); // Cookie valid for 1 hour
}
echo "Welcome, $username";
}
?>

3. Displaying User Data:
   php

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   <?php
if (isset($_COOKIE["username"])) {
echo "Welcome back, " . $_COOKIE["username"];
} else {
echo "Please log in.";
}
?>


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Activities and Exercises

1. Cookies:
   • Create a script to set a cookie for the user’s preferred language. Display a greeting in that language on subsequent visits.
2. Sessions:
   • Build a shopping cart system using sessions where users can add, view, and clear items.
3. Combination:
   • Create a login system that uses sessions for authentication and cookies for remembering the username.

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Assignment

1. Part 1: Using Cookies
   • Create a form where users can input their favorite color.
   • Save the color in a cookie and display the page’s background in that color when revisited.
2. Part 2: Using Sessions
   • Create a multi-page application:
     1. A form on Page 1 collects the user’s name.
     2. Page 2 displays a personalized greeting using session data.
     3. A logout button on Page 3 clears the session.

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Summary

In this lesson, you learned how to:

1. Set, retrieve, and delete cookies in PHP.
2. Work with sessions to manage user data across multiple pages.
3. Understand the differences and use cases for cookies and sessions.

These skills are essential for creating dynamic, user-focused web applications. Let me know if you’d like additional examples or exercises!