excell-csv-output.php

<?php

function excell_arr2csv($header, $data) {
	$line = '';

	foreach ($header as $field) {
		$d = isset($data[$field]) ? $data[$field] : '';

		$d = str_replace("\n", " ", $d);
		$d = str_replace('"', '""', $d);

		# http://georgemauer.net/2017/10/07/csv-injection.html

		if (in_array(substr($d, 0, 1), ['=', '-', '+', '@'], true)) {
			$d = "\t" . $d;
		}

		if ($line != '') $line .= ',';
		$line .= '"' . $d . '"';
	}

	return $line;
}

function excell_csv_output($output_file, $header, $data) {

	$fp = fopen($output_file, "w+");

	fwrite($fp, "\xEF\xBB\xBF");

	$header_keys = array_keys($header);

	fwrite($fp, excell_arr2csv($header_keys, $header) . "\r\n");

	foreach ($data as $row) {
		fwrite($fp, excell_arr2csv($header_keys, $row) . "\r\n");
	}

	fclose($fp);

}

test.php

<?php

include_once dirname(__FILE__) . '/excell-csv-output.php';

$output_file = "t1.csv";

$header = array('a' => 'a', 'b' => 'b');

$data = [
	['a' => 'aaa', 'b' => '4+4'],
	['a' => 'bbb', 'b' => '=4+4'],
	['a' => 'ccc', 'b' => ''],
];

excell_csv_output($output_file, $header, $data);