What are common reasons for a PHP script to mistakenly assume a user is not logged in due to session handling issues?

Common reasons for a PHP script to mistakenly assume a user is not logged in due to session handling issues include expired sessions, incorrect session variables, or session data not being properly saved or retrieved. To solve this issue, make sure to properly set session variables upon login and check for them on subsequent pages to verify the user's login status. Additionally, ensure that session_start() is called at the beginning of each page where session variables are needed. 

// Start the session
session_start();

// Check if the user is logged in
if(isset($_SESSION['user_id'])) {
    // User is logged in
} else {
    // User is not logged in
    // Redirect to login page or display an error message
}

Keywords

session handling PHP script user login authentication session variables

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