How to remove warning Cannot modify header information - headers already sent by

Question

A "headers already sent" warning arises .I close $zip->close(); but still show warning

$zip = new ZipArchive;
$download = 'new_zip.zip';
$zip->open($download, ZipArchive::CREATE);
foreach (glob("zipfile/*") as $file) { 
    $zip->addFile($file);
}
$zip->close();
header('Content-Type: application/zip');
header("Content-Disposition: attachment; filename = $download");
header('Content-Length: ' . filesize($download));
header("Location: $download");

Answer 1

At the start of your script, use:

<?php ob_start(); ?>

Then at the end of your script, add:

<?php ob_flush(); ?>