How can headers already sent affect the behavior of session variables in PHP?

Headers already sent can affect the behavior of session variables in PHP because session_start() must be called before any output is sent to the browser. If headers are sent before session_start(), PHP will not be able to set the necessary session cookies, resulting in session variables not being saved or retrieved properly. To solve this issue, ensure that session_start() is called before any output is sent, such as HTML, whitespace, or even error messages. 

<?php
// Start the session before any output is sent
session_start();

// Rest of your PHP code here
?>

Keywords

headers session variables behavior PHP error

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