！isset使用有效变量返回FALSE？ [重复]

Question

This question already has an answer here:

• Reference — What does this symbol mean in PHP? 18 answers

I'm trying to add a bit more security to my website process so that an external user who tries to bypass the login page will run into an !isset that checks whether the login $_SESSION variables are set and if not, destroys the session and redirects back to the main login page.

My problem is that the !isset function returns a FALSE value and thus destroys the session and redirects, but when I test the variables on that page with print_r they are being recognized and stored.

My code (I've blanked out the variables):

<?php  

 session_start();

 if(!isset($_SESSION['xxx'], $_SESSION['xxx']))
  { echo "Login successfull"; }

  else 

  { session_destroy();
    header("location:main_login.php");
  }

?>

If anyone could explain me what I did wrong (not even necessarily give me the answer on paper, I like to understand and learn since I'm a rookie) that would be amazing. I tried looking around but couldn't really find what I was looking for. Many thanks in advance!

</div>

Answer 1

if(!isset($_SESSION['xxx'], $_SESSION['xxx']))

This is checking if the session is not set, note the ! symbol. So you are echoing Login Successfull when the session variables are not set.

You should have it like the following:

if(isset($_SESSION['xxx'], $_SESSION['xxx']))
{ 
    echo "Login successfull"; 
}
else 
{ 
    session_destroy();
    header("location:main_login.php");
}