notes-shivam

unit 4

3 min read

Working with Cookies and Sessions in PHP

1. Cookies in PHP

1.1 Introduction to Cookies

  1. A cookie is a small piece of data stored in the user’s browser.

  2. Used to:

    • Store user preferences

    • Track users

    • Maintain state across requests

  3. Cookies are stored client-side (browser).

1.2 Setting Cookies in PHP

Syntax

setcookie(name, value, expiry, path, domain, secure, httponly);

Example

<?php
setcookie("username", "Shivam", time() + 3600); // expires in 1 hour
?>

Important Points

  1. Must be called before any HTML output

  2. time() + 3600 → expiry in seconds

1.3 Accessing Cookies

<?php
if (isset($_COOKIE['username'])) {
    echo "Welcome " . $_COOKIE['username'];
}
?>

1.4 Deleting Cookies

Method: Set expiry in past

<?php
setcookie("username", "", time() - 3600);
?>

1.5 Advantages and Limitations

Advantages

  1. Simple to use

  2. Stored on client side

Limitations

  1. Limited size (~4KB)

  2. Less secure (can be modified by user)

2. Sessions in PHP

2.1 Introduction to Sessions

  1. Session stores data on the server.

  2. Each user is assigned a unique session ID.

  3. Used for:

    • Login systems

    • Shopping carts

    • Secure data storage

2.2 Starting a Session

Syntax

session_start();

Example

<?php
session_start();
?>

Important Rule

  1. Must be called before any HTML output

2.3 Working with Session Variables

Setting Session Variable

<?php
session_start();
 
$_SESSION['username'] = "Shivam";
?>

Accessing Session Variable

<?php
session_start();
 
echo $_SESSION['username'];
?>

Checking Session Variable

<?php
if (isset($_SESSION['username'])) {
    echo "Logged in";
}
?>

2.4 Passing Session IDs in Query String

  1. Session ID can be passed manually in URL.

Example

<?php
session_start();
 
echo session_id();
?>

URL example:

page.php?PHPSESSID=abc123

Note

  1. Used when cookies are disabled

  2. Not recommended due to security risks

2.5 Destroying Sessions

1. Unset Specific Variable

<?php
unset($_SESSION['username']);
?>

2. Destroy Entire Session

<?php
session_start();
session_destroy();
?>

2.6 Complete Session Cleanup

<?php
session_start();
 
session_unset();  // remove all variables
session_destroy(); // destroy session
?>

2.7 Using Sessions (Login Example)

<?php
session_start();
 
$_SESSION['user'] = "Shivam";
 
echo "Session started for " . $_SESSION['user'];
?>

3. Cookies vs Sessions

3.1 Differences

  1. Storage:

    • Cookies → Client-side

    • Sessions → Server-side

  2. Security:

    • Cookies → Less secure

    • Sessions → More secure

  3. Size:

    • Cookies → Limited

    • Sessions → Larger data

4. Complete Working Program

Problem: Simple Login System using Cookies and Sessions

<?php
session_start();
 
// If form submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
 
    $username = $_POST['username'];
 
    // Set session
    $_SESSION['user'] = $username;
 
    // Set cookie (valid for 1 hour)
    setcookie("user", $username, time() + 3600);
 
    echo "Login successful!<br>";
}
 
// Show session data
if (isset($_SESSION['user'])) {
    echo "Session User: " . $_SESSION['user'] . "<br>";
}
 
// Show cookie data
if (isset($_COOKIE['user'])) {
    echo "Cookie User: " . $_COOKIE['user'] . "<br>";
}
 
// Logout
if (isset($_GET['logout'])) {
    session_unset();
    session_destroy();
 
    setcookie("user", "", time() - 3600);
 
    echo "Logged out successfully";
}
 
?>
 
<!-- HTML Form -->
<form method="POST">
    Username: <input type="text" name="username"><br>
    <input type="submit" value="Login">
</form>
 
<a href="?logout=true">Logout</a>

5. Quiz (Exam Practice)

Small data stored in browser.

Q2. Which function is used to start a session?

session_start()

Q3. Where are sessions stored?

Server-side

Set expiry time in past.

Q5. Which is more secure: cookies or sessions?

Sessions

6. Summary

6.1 Cookies

  1. Stored in browser

  2. Use setcookie()

  3. Limited and less secure

6.2 Sessions

  1. Stored on server

  2. Use session_start()

  3. Secure and widely used

6.3 Key Functions

  1. Cookies:

    • setcookie()

    • $_COOKIE

  2. Sessions:

    • session_start()

    • $_SESSION

    • session_destroy()

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