How can the placement of functions like session_start() and header() affect the execution of PHP scripts, especially in the context of user authentication?

The placement of functions like session_start() and header() in PHP scripts is crucial, especially in the context of user authentication. session_start() should be called before any output is sent to the browser, and header() should be called before any actual output is sent. This ensures that the session data is properly initialized and headers are set before any content is displayed to the user. 

<?php
session_start();

// Perform user authentication
if($authenticated){
    $_SESSION['user'] = $username;
    header("Location: dashboard.php");
    exit();
} else {
    header("Location: login.php");
    exit();
}
?>

Keywords

session_start header user authentication execution order PHP scripts

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