What is the significance of the error message "Cannot modify header information - headers already sent" in PHP development?

The error message "Cannot modify header information - headers already sent" in PHP development indicates that there was output sent to the browser before PHP tried to modify header information, such as setting cookies or changing the content type. This can happen if there is whitespace or any other output (like HTML or text) before the header function calls in your PHP script. To solve this issue, make sure there is no output sent to the browser before modifying header information. 

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

// Your PHP code here

ob_end_flush(); // Flush the output buffer

Keywords

PHP header output buffering ob_start error message

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