What are some common causes of the "header already sent" error in PHP?

The "header already sent" error in PHP occurs when there is output sent to the browser before the header() function is called to set HTTP headers. This can be caused by whitespace or characters outside of the PHP tags in the file, or by calling functions like echo or print before setting headers. To solve this issue, make sure to move the header() function calls to the top of the file before any output is sent. 

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

// Place header() function calls at the top of the file
header('Content-Type: text/html');

// Rest of the PHP code goes here

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

Keywords

output buffering whitespace include echo warning

Related Questions