在PHP中訪問會話數(shù)據(jù)需先啟動會話，再通過$_SESSION超全局數(shù)組進行操作。1. 啟動會話必須使用session_start()，且該函數(shù)需在任何輸出前調(diào)用；2. 訪問會話數(shù)據(jù)時應(yīng)檢查鍵是否存在，可使用isset($_SESSION['key'])或array_key_exists('key', $_SESSION)；3. 設(shè)置或更新會話變量只需對$_SESSION數(shù)組賦值，無需手動保存；4. 清除特定數(shù)據(jù)可用unset($_SESSION['key'])，清空所有數(shù)據(jù)可設(shè)$_SESSION為空數(shù)組，徹底結(jié)束會話還需調(diào)用session_unset()和session_destroy()，同時注意手動刪除客戶端的會話Cookie以完成清理。

In PHP, accessing session data is straightforward once the session has been started. The key is to use the $_SESSION superglobal array, which holds all session variables you've set.

Starting a Session

Before you can access or store any session data, you need to start the session using session_start(). This function must be called before any output is sent to the browser — even a blank line or space counts.

<?php
session_start();
?>

A common mistake is forgetting to call this at the top of every page where you want to access session data. Also, don't put anything (including HTML or echo statements) before the <?php tag if you're using session_start() there.

Accessing Stored Session Data

Once the session is started, you can access stored values just like you would with any associative array:

echo 'Welcome back, ' . $_SESSION['username'];

Make sure the key exists before trying to access it — otherwise, you might trigger a notice or warning.

Here’s how to safely check for a session variable:

• Use isset($_SESSION['key']) to see if it's been set
• Or use array_key_exists('key', $_SESSION) if you want to distinguish between null and not-set

If you're debugging or just want to see what's in the session, print_r($_SESSION); can help.

Setting and Updating Session Variables

You can add or update session data anytime after starting the session:

$_SESSION['user_id'] = 123;
$_SESSION['logged_in'] = true;

These will persist across requests as long as the session is active. If you change a value later in the script, the session will hold the updated version.

One thing to note:

You don’t have to "save" the session manually — PHP handles that automatically when the script ends.

Destroying or Clearing Session Data

To remove specific data, use unset():

unset($_SESSION['user_id']);

To clear everything in the session:

$_SESSION = [];

And if you want to completely end the session (like during logout), you should also call session_destroy():

session_unset();
session_destroy();

Keep in mind that session_destroy() only removes the data on the server — you still need to unset the session cookie on the user’s side for full cleanup.

基本上就這些。

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