问如何使用PHP创建会话？

EN

session_start(); //Start the session.  Call on every page that will have the login.
$login = $_POST['login'];
$pass = $_POST['pass'];  //Get login and password the user has sent.

if (is_valid_user($login, $pass)) {
   //If user is valid, pass them along to the next page.
   $_SESSION['logged_in_user'] = $login; //Keep track of the username in the session
}
else echo "Not a valid login";

session_start();

if(isLoginCorrect())
{
    $_SESSION['logged_in'] = true;
}

<?php if($_SESSION['logged_in']): ?>
    You are logged in
<?php else: ?>
    You aren't logged in
<?php endif; ?>