补全Y-M-D日期

无须考虑 不同年份，不同月份

$start = '2019-01-01';
$end = '2020-09-02';
function printDates($start, $end)
{
    $num = 0;
    $dt_start = strtotime($start);
    $dt_end = strtotime($end);
    while ($dt_start <= $dt_end) {
        $data[$num]['date'] = date('Y-m-d', $dt_start);
        $data[$num]['value'] = 0;
        $dt_start = strtotime('+1 day', $dt_start);
        $num++;
    }
//var_dump($data);
    return $data;
}