What precautions should be taken to prevent "Cannot add header information - headers already sent" errors in PHP?

The "Cannot add header information - headers already sent" error in PHP occurs when there is output sent to the browser before headers are set using functions like header(). To prevent this error, make sure to set headers before any output is sent to the browser, including whitespace or HTML tags. 

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

// Set headers before any output
header('Content-Type: text/html');

// Your PHP code here

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

Keywords

output buffering ob_start ob_end_flush header error_reporting

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