PHP Session会话

<?php
   session_start();

   if (isset($_SESSION['counter'])) {
      $_SESSION['counter']++;
   } else {
      $_SESSION['counter'] = 1;
   }


   $msg = "You have visited this page ".  $_SESSION['counter'];
   $msg .= "in this session.";

   echo ( $msg );
?>

<p>
   To continue  click following link <br />

   <a  href = "nextpage.php?<?php echo htmlspecialchars(SID); ?>">
</p>