Why do certain echo statements in PHP code cause "Headers already sent" errors while others do not?

The "Headers already sent" error occurs when PHP tries to send HTTP headers, but there has already been output sent to the browser before the headers are set. This commonly happens when there is whitespace or HTML content before the PHP opening tag or when there are multiple echo statements before setting headers. To solve this issue, make sure there is no output sent before setting headers, and consolidate any echo statements before sending headers. 

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

// Place all PHP code before any output is sent
// This includes any HTML, whitespace, or echo statements

ob_end_flush(); // Flush the output buffer and send content to the browser
// Set headers after all output has been processed
header('Location: example.php');
exit; // Terminate script execution
?>

Keywords

echo PHP code Headers already sent errors functions

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