Basic usage

<?php

ob_start();
echo "Hello\n";

setcookie("cookiename", "cookiedata");

ob_end_flush();

?>

In the above example, the output from echo would be stored in the output buffer until ob_end_flush was called. In the mean time, the call to setcookie successfully stored a cookie without causing an error. (Headers cannot normally be sent to the browser after data has already been sent.)