PHP 输出两个指定日期之间的所有日期

function printDates($start,$end){
$dt_start = strtotime($start);
$dt_end = strtotime($end);
while ($dt_start<=$dt_end){
echo date('Y-m-d',$dt_start)."<br>";
$dt_start = strtotime('+1 day',$dt_start);
}
}
printDates('2019-1-1','2019-07-05');