login.php

<?php
session_start();

$user = $_GET["user"];
$session_ID = session_id();
$_SESSION[$session_ID]=$user;

print $session_ID;

登陸後返回sessionID

http://localhost/login.php?user=root

用戶執行一些需要已經在登陸狀態的操作

帶上sessionID

http://localhost/islogin.php?sessionID=a3dms2f84b55i2pg9r2gffm0v5

我們可以通過sessionID來判斷是哪個用戶

islogin.php

<?php
session_start();
$session_id = $_GET[‘sessionID‘];
if (isset($_SESSION[$session_id])){
    print $_SESSION[$session_id] ;

} else{
    print ("未登陸");
}

用戶註銷時也註銷sessionID

loginout.php

<?php

session_start();

session_id = _GET[‘sessionID‘];

session_unset($session_id);

訪問loginout後

http://localhost/loginout.php?sessionID=a3dms2f84b55i2pg9r2gffm0v5

再次判斷是否登陸

http://localhost/islogin.php?sessionID=a3dms2f84b55i2pg9r2gffm0v5

根據sessionID判斷用戶是否登陸