php 日期比较函数

$date1 = '2023-10-01';
$date2 = '2023-10-15';

if (strtotime($date1) < strtotime($date2)) {
    echo "$date1 is before $date2";
} else {
    echo "$date1 is after or equal to $date2";
}

$date1 = new DateTime('2023-10-01');
$date2 = new DateTime('2023-10-15');

if ($date1 < $date2) {
    echo "$date1 is before $date2";
} else {
    echo "$date1 is after or equal to $date2";
}

$date1 = '01-10-2023';
$date2 = '15-10-2023';

$date1 = DateTime::createFromFormat('d-m-Y', $date1);
$date2 = DateTime::createFromFormat('d-m-Y', $date2);

if ($date1 < $date2) {
    echo "$date1 is before $date2";
} else {
    echo "$date1 is after or equal to $date2";
}

$date1 = new DateTime('2023-10-01', new DateTimeZone('UTC'));
$date2 = new DateTime('2023-10-15', new DateTimeZone('UTC'));

if ($date1 < $date2) {
    echo "$date1 is before $date2";
} else {
    echo "$date1 is after or equal to $date2";
}