问在PHP页面之间传输变量

EN

<?php
session_start();

if (isset($_POST['username'], $_POST['password']) {
    $_SESSION['username'] = $_POST['username'];
    $_SESSION['password'] = $_POST['password'];
    echo '<a href="nextpage.php">Click to continue.</a>';
} else {
    // form
}
?>

<?php
session_start();

if (isset($_SESSION['username'])) {
    echo $_SESSION['username'];
} else {
    header('Location: index.php');
}
?>

//page1.php
session_start();
$_SESSION['user']='user';
$_SESSION['password']='password';

//page2.php
session_start();
echo $_SESSION['user'] . ' ' . $_SESSION['password'];