Introduction

Cookies are small pieces of data stored in the user’s browser. Unlike sessions, which store data on the server, cookies store information on the client’s device.

Cookies help websites remember users even after they close and reopen their browser.

They are widely used for:

• Remember Me login
• Dark mode preference
• Language selection
• Shopping cart preferences
• Recently viewed products
• User personalization

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What is a Cookie?

A cookie is a small text file created by the server and stored in the browser.

When the user visits the website again, the browser sends the cookie back to the server.

This allows PHP to recognize returning visitors.

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How Cookies Work

1. User visits the website.
2. PHP creates a cookie.
3. Browser stores the cookie.
4. User revisits the website.
5. Browser sends the cookie back automatically.
6. PHP reads the stored value.

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Creating a Cookie

Use the setcookie() function.

<?php

setcookie(
    "username",
    "Malik",
    time() + 86400,
    "/"
);

echo "Cookie Created";

?>

This cookie expires after 1 day.

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Reading a Cookie

<?php

if(isset($_COOKIE["username"])){

    echo "Welcome " . $_COOKIE["username"];

}

?>

Output

Welcome Malik

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Updating a Cookie

Simply create the cookie again with a new value.

<?php

setcookie(
    "username",
    "Adil",
    time()+86400,
    "/"
);

?>

The old value is replaced.

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Deleting a Cookie

To delete a cookie, set its expiration time to the past.

<?php

setcookie(
    "username",
    "",
    time()-3600,
    "/"
);

?>

The browser removes the cookie.

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Cookie Lifetime

Common expiration examples:

• 1 hour

time() + 3600

• 1 day

time() + 86400

• 30 days

time() + (86400 * 30)

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Real-World Example

Remember the user’s preferred theme.

<?php

setcookie(
    "theme",
    "dark",
    time()+86400*30,
    "/"
);

?>

Later:

<?php

if(isset($_COOKIE["theme"])){

    echo "Theme: " . $_COOKIE["theme"];

}

?>

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Cookies vs Sessions

Cookies	Sessions
Stored in browser	Stored on server
Can persist for days/months	Usually expire when session ends
Limited storage	Larger storage
User can delete them	Managed by server
Best for preferences	Best for authentication

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Security Tips

• Never store passwords in cookies.
• Use HTTPS.
• Enable the HttpOnly flag for sensitive cookies.
• Use the Secure flag on HTTPS sites.
• Validate cookie values before using them.

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Common Mistakes

❌ Storing confidential information

❌ Creating cookies after HTML output

❌ Assuming cookies always exist

❌ Trusting cookie values without validation

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Frequently Asked Questions

Where are cookies stored?

In the user’s web browser.

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Can users delete cookies?

Yes. Users can clear cookies from browser settings.

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Are cookies secure?

Cookies are useful but should never store sensitive information such as passwords or payment details.

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Conclusion

Cookies help websites remember users, preferences, and settings across multiple visits. Combined with PHP Sessions, they form the backbone of personalization and authentication in modern web applications.

Understanding cookies is essential for building user-friendly PHP websites.

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Next Tutorial

PHP File Upload Explained with Examples (2026 Guide)