Session_start不起作用或Session_destroy不起作用？

Question

I have this code in a default index page:

<?php 
$_SESSION['user'] = 'Bill';
print $_SESSION['user'];

$_SESSION = array();
session_destroy();

$_SESSION['user'] = 'Andy';
print $_SESSION['user'];
?>

The output is the following:

Bill
Warning: session_destroy(): Trying to destroy uninitialized session in C:\xampp\htdocs\DSP\index.php on line 15
Andy

Obviously I have to initialize the session with session_start() but these are my questions:

1) However, why can I store a session without session_start() function?

2) Now I put session_start() function on the top of the code:

<?php 
session_start();

$_SESSION['user'] = 'Bill';
print $_SESSION['user'];

$_SESSION = array();
session_destroy();

$_SESSION['user'] = 'Andy';
print $_SESSION['user'];
?>

Now the output is the following:

Bill
Andy

My question now is:

3) Why Andy is printed on the output? Why compiler NOT gives me error that session must be started again beacuse I destroyed it before with the command session_destroy()?

Thanks everyone very much!

Answer 1

However, why can I store a session without session_start() function?

Because it's just a usual array and can be accessed as such. It is same with $_POST, $_GET and other super-global arrays. However, the session is only created after you call session_start(), so trying to store information in the array before initializing the session is pointless.

I don't see anything unusual in your code and the output produced. To illustrate, see the following code:

<?php 
session_start();

$_SESSION['user'] = 'Bill';    
var_dump($_SESSION);

$_SESSION = array();
session_destroy();    
var_dump($_SESSION);

$_SESSION['user'] = 'Andy';
var_dump($_SESSION);

The output is:

array(1) {
  ["user"]=>
  string(4) "Bill"
}

array(0) {
}

array(1) {
  ["user"]=>
  string(4) "Andy"
}

This is what happens above:

• Session is initialized using session_start()
• A string Bill with the key user is added to the associative array
• session_destroy() destroys the session data that is stored in the session storage. ($_SESSION is now empty)
• Another string Andy with the key user is added to the associative array

As you'd expect, the output would be Andy. I don't see the issue?