What is the common error message "Warning: Cannot modify header information - headers already sent" in PHP and how can it be resolved?

The common error message "Warning: Cannot modify header information - headers already sent" in PHP occurs when there is whitespace or output before the header() function is called, which prevents headers from being sent to the browser. To resolve this issue, make sure there is no output (including whitespace) before the header() function is called, and avoid using functions like echo or print before sending headers. 

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

// Your PHP code here

ob_end_clean(); // Clean the output buffer without sending its contents

// Now you can safely call header() function without any issues
header("Location: https://www.example.com");
exit;
?>

Keywords

PHP header output buffering ob_start error message

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