PHP Warning: session_start(): Cannot start session when headers already sent

Question

Im getting an error in my wp-debug log saying "PHP Warning: session_start(): Cannot start session when headers already sent in ...hooks.php on line 228". Here is a code snippet from the file

function _action_fw_flash_message_backend_prepare() {
            if ( ! session_id() ) {
                session_start();    
            }
        }

session_start(); is on 228. I have read that session_start should be the first line of code to be executed in the file. Will this not affect the functionality of the code? (I have zero PHP experience)

Answer 1

Move the session_start() to top of the page. and ob_flush();in footer or end of the script.

<?php
@ob_start();
session_start();
?>