session_start(): Cannot start session when headers already sent in /storage/ssd4/734/16803734/public_html/navbar.php on line 2 code example

Example: session_start(): cannot start session when headers already sent

// FIRST line of each php file using session (no character before)
<?php if ( empty(session_id()) ) session_start(); ?>
// Encode in ANSI or UTF8 (No BOM !)