What potential issues can arise when modifying header information in PHP, as seen in the warning message provided?

Modifying header information in PHP can lead to warnings like "Cannot modify header information - headers already sent." This typically occurs when there is output (such as HTML, whitespace, or error messages) 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: http://www.example.com"); // Redirect header

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

Keywords

header PHP modification warning message security

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