Why is it important not to have any output before calling session_start() in PHP?

Having any output before calling session_start() in PHP can lead to headers already being sent to the browser, which can cause errors such as "Headers already sent" or session data not being saved properly. To solve this issue, make sure there is no output (including whitespace) before calling session_start(). 

<?php
// Ensure there is no output before calling session_start()
ob_start();
session_start();

// Rest of your PHP code here
?>

Keywords

session_start output buffering headers_sent session variables PHP session management

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