What are some potential causes for the error message "Cannot modify header" in PHP scripts?

The error message "Cannot modify header information - headers already sent" in PHP scripts typically occurs when there is whitespace or output sent before the header() function is called. To solve this issue, make sure there is no output (including spaces, HTML, or PHP errors) before calling the header() function. 

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

// Your PHP code here

header("Location: https://www.example.com"); // Redirect header

ob_end_flush(); // Flush output buffer
?>

Keywords

header modification output buffering ob_start headers_sent

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