a.php:
....
session_start();
session_register(uid,pwd);
$_SESSION['uid']="aaa";
$_SESSION['pwd']="bbb";
header("Location:b.php");
....

b.php:
...
session_start();
$uid = $_SESSION["uid"];
$pwd = $_SESSION["pwd"];
...

但是b.php的$uid和$pwd都是空的，而不是aaa和bbb，请老大指点，谢谢了！