What are common causes of the "header already sent" error in PHP scripts?

The "header already sent" error in PHP scripts occurs when there is output (such as echoing text or whitespace) before the header function is called. To solve this issue, make sure to call the header function before any output is sent to the browser. 

<?php
ob_start(); // Start output buffering

// Your PHP code here

header('Location: new_page.php'); // Redirect to a new page

ob_end_flush(); // Flush the output buffer and send output to the browser
?>

Keywords

output buffering whitespace include echo ob_start

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