我正在尝试验证$ _SESSION的状态以允许访问网页，但它无法正常工作

The page that has the following code will only redirect:

Here is the code I am trying to include at the top of other pages that I want to check S_SESSION before allowing access:

<?php
session_start();
include ('connect_SQL_DB.php');
include('header.html');

if(!isset($_SESSION['login']) || (trim($_SESSION['login'])=='')) {
header('location:login_redirect.php');
exit();
} 
?>

Here js my code for the login page:

<?php
session_start();
include ('connect_SQL_DB.php'); 
include('header.html');

print '<h2>Login Form</h2>
    <p>Users who are logged in can view and make changes to the website.</p>';

if ($_SERVER['REQUEST_METHOD'] == 'POST') {

    if ( (!empty($_POST['email'])) && (!empty($_POST['password'])) ) {

        $query=mysql_query("SELECT * FROM account WHERE email= '"
        . $_POST['email'] . "'

        AND password= '" . $_POST['password'] . "'

        AND enabled='1'") or die (mysql_error());

        $check = mysql_num_rows($query);

        if ($check > 0) {

            $row = mysql_fetch_array($query, MYSQL_ASSOC);

                $user = array(
                'userid' => $row['userid'],
                'email' => $row['email'],
                'accesslevel' => $row['accesslevel'],
                'password' => md5 ($row['password']), 
                'enabled' => $row['enabled'],
                );      



            //Session
            session_start();
            $_SESSION['login'][] = $user;
            header('location:message.php');
            ob_end_clean();
            exit();

        } else {

            header('location:login_redirect.php');



        }

    } else {

    print '<p>Please make sure you enter both an email address and a password!<br />Go
    back and try again.</p>';

    }

} else {

    print '<form action="login.php" method="post">
    <p>Email Address: <input type="text" name="email" size="20" /></p>
    <p>Password: <input type="password" name="password" size="20" /></p>
    <p><input type="submit" name="submit" value="Log In!" /></p>
    </form>';

}

include('footer.html');
?>

Its not working because header already sent when you include header.html

Always put your redirect logic on above any print statement.

Try to put following code on every page.

<?php
session_start();
if(!isset($_SESSION['login']) || (trim($_SESSION['login'])=='')) {
header('location:login_redirect.php');
exit();
}
include ('connect_SQL_DB.php');
include('header.html');


?>