使用PHP会话变量来保持用户登录网站

Question

I want to assign a value to a session variable when a user logs into a website. I read that I must explicitly start a session at the top of my pages in order to do this. So I inserted:

if (!isset($_SESSION)){
    session_start();
    echo "started";
}

The first thing I notice is that "started" is displayed every time I reload my page. Is that expected behavior? I would assume the second time I load the page, the session should already be there, therefore "started" would not display.

Further down in my page, I have:

$_SESSION['id']=2;
echo "<p>Your session ID is: " . $_SESSION['id'] . "</p>";

That correctly displays the ID in the "echo" statement. So even after assigning a value to a session variable, when I reload the page, it puts "started" at the top.

Am I doing something wrong? Thank you!

Answer 1

That is expected behaviour, you need to call session_start() before any output is sent to the browser every time the page is loaded, which is why your echo is happening every time. You if statement in this case is a little unnecessary and you should just simply call it without the if.

session_start();

For example, a $_SESSION variable will never be accessible unless you call session_start(), despite the fact that it will exist in the browser's session. Calling session_start() simply allows you to access that superglobal array.