Setting cookies in PHP requires correctly using the setcookie() function and pay attention to key details, otherwise it may cause abnormal functions. Its basic syntax is setcookie('name', 'value', expiration, path, domain, secure, httponly), and the parameters represent name, value, expiration time, path, domain name, security flag and HttpOnly flag respectively. It is necessary to ensure that the setcookie() is called before any output, otherwise it will fail because the HTTP header has been sent; after setting the cookie, it cannot be read immediately through $_COOKIE, and you need to wait for the next request; when deleting the cookie, it must set its expiration time to the past time point, and ensure that the path and domain name are consistent with the setting time, otherwise it may not be deleted correctly.

Setting a cookie in PHP is pretty straightforward using the setcookie() function. But there are some important details to get right, or it might not work the way you expect.

Basic Syntax and Usage

The most basic way to set a cookie looks like this:

 setcookie('name', 'value', time() 3600, '/', 'example.com', true, true);

This sets a cookie that lasts for one hour. The parameters after the value include expiration time, path, domain, secure flag, and httponly flag. All of these help control how and where the cookie is used.

You should always make sure the expiration time is set correctly — if you don't, the cookie will expire when the browser closes.

Here's what each part means:

• Name : What your cookie is called.
• Value : The data you want to store.
• Expiration : When the cookie should be deleted (in seconds since the Unix epoch).
• Path : Which paths on your site can access the cookie.
• Domain : Which domain the cookie is available to.
• Secure : If true, the cookie will only be sent over HTTPS.
• HttpOnly : If true, JavaScript won't be able to access the cookie.

Common Pitfalls and How to Avoid Them

A lot of people run into issues because they forget that setcookie() must be called before any output is sent to the browser — including whitespace or HTML. If you see an error about headers already sent, that's probably why.

Also, pay attention to the path and domain settings. For example, if you're setting a cookie on www.example.com but trying to read it on blog.example.com , it won't be available unless you set the domain properly (like .example.com ).

Another thing: cookies aren't immediately available after setcookie() is called. You'll need to wait until the next request to access them via $_COOKIE .

Reading and Deleting Cookies

To read a cookie, just use the $_COOKIE superglobal array:

 if (isset($_COOKIE['name'])) {
    echo 'Cookie value: ' . $_COOKIE['name'];
}

Deleting a cookie isn't done directly — instead, you set its expiration time in the past:

 setcookie('name', '', time() - 3600, '/');

This tells the browser to remove the cookie. Make sure the path and domain match what was used when setting it, or it might not delete properly.

That's basically it. It seems simple, but small mistakes with timing, paths, or domains can cause problems.

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