“session_start(): Cannot send session cache limiter - headers already sent” keep coming even after session_start() already on top

Question

I got "Warning: session_start(): Cannot send session cache limiter - headers already sent". I cannot put the session_start() on top because i'm using "use Phppot\DataSource" and it will not work if i change their position. The code that i made was like this:

<?php
use Phppot\DataSource;
session_start();
require_once 'web.php';
?>

Can someone help me solve this error? Thanks!

Answer 1

move session_start() under <?php

sessions and other headers have to be set before anything is broadcasted, and it seems phppot is broadcasting something looking at the error.

Answer 2

You can actually check what is causing headers to be sent: https://www.php.net/manual/en/function.headers-sent.php

So for debugging you could do something like

<?php
use xxx;

if (headers_sent($file, $line)) {
    die("Headers unexpectedly sent from {$file}::{$line}");
}
session_start();

Note that session_start() as your first statement is generally not the proper solution to these kinds of issues...