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

The error message "Cannot modify header information - headers already sent by" in PHP indicates that there was output (such as echo, print, whitespace, or HTML) sent to the browser before the header function was called. To solve this issue, make sure that there is no output sent to the browser before using header functions like header() or setcookie(). 

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

// Your PHP code here

ob_end_clean(); // Clean the output buffer without sending any data

// Now you can safely use header functions
header('Location: newpage.php');
?>

Keywords

PHP header error message headers already sent significance

Related Questions