<?php
/**
 * @param  object $obj ( may be array )
 * @return mixed  string or null
 */
function csv_encode($obj)
{
    $csv  = null;
    $rows = is_object($obj) ? json_decode(json_encode($obj), true) : $obj;

    if ( $rh = fopen('php://memory', 'w') ) {
        fputcsv($rh, array_keys($rows[0]));

        foreach ( $rows as $row ) {
            fputcsv($rh, array_values($row));
        }

        rewind($rh);
        $csv = stream_get_contents($rh);
        fclose($rh);
    }

    return $csv;
}