What are common causes of the "Cannot modify header information" error in PHP?

The "Cannot modify header information" error in PHP occurs when there is output sent to the browser before PHP attempts to modify header information, such as using functions like header() or setcookie(). To solve this issue, make sure there is no output (including whitespace) before calling header() or setcookie(). You can also use ob_start() at the beginning of your script to buffer the output and prevent this error. 

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

// Your PHP code here

header('Location: newpage.php'); // Example of modifying header information

ob_end_flush(); // Flush the output buffer
?>

Keywords

header information error PHP output buffering ob_start

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