PHP Fputcsv header not showing - php

Question

I am trying to create a csv in php with products from magento but my header doesn't show up in the csv file, just the products.
If i put the fputcsv for the headings inside the foreach it display the header then one product then the header again and another product and so on...
##### Print product data ####################################################
$headings = ['category', 'manufacturer', 'productid', 'identifier', 'name', 'description', 'product_url', 'image_url', 'price','show_product', 'availability', 'delivery_cost'];
$fh = fopen('php://output', 'w');
ob_start();
fputcsv($fh, $headings);
foreach($ALL_PRODS as $productId) {
// If we've sent this one, skip the rest - this is to ensure that we do not get duplicate products
if (#$already_sent[$productId] == 1) continue;
$PRODUCT = array();
$PRODUCT = smfeed_get_product_details($productId);
if ($PRODUCT['show_product'] == 1 ) {
fputcsv($fh, $PRODUCT);
$string = ob_get_clean();
$filename = 'csv_' . date('Ymd') . '_' . date('His');
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private", false);
header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename=\"$filename.csv\";");
header("Content-Transfer-Encoding: binary");
$prod_count ++;
// Debuging
if (isset($_GET['debug'])) {
$cnt_prod ++;
if (#$_GET['stats'] == "off") {
}
else {
echo $cnt_prod . ".";
echo "\t" . number_format(microtime(true) - $time, 3) . "s \n";
$time = microtime(true);
echo "\t" . number_format(memory_get_usage()/1048576, 3) . "Mb\n";
}
}
// Limit displayed products
if ($limit > 0 && $prod_count >= $limit && !isset($_GET['pg'])) {
// Debuging
if (isset($_GET['debug'])) {
echo "\n" . $cnt_prod . "products displayed \n";
echo "\npage loaded in " . number_format(microtime(true) - $time_start, 3) . "s \n";
echo number_format(memory_get_usage()/1048576, 3) . "Mb\n";
}
exit;
}
}
$already_sent[$productId] = 1;
}
exit($string);

Answer 1

ob_start(); starts output buffering.
Buffer contains the header line.
After the first product output is done, output buffering is ended by ob_get_clean();
Since $string = ob_get_clean(); assignment is called in the loop, its content being rewritten by false value (since the buffering was ended before) therefore final exit($string); does not output anything.
There are many other issues in your code. For example, HTTP headers will be set over again and again for each item in the loop.