php 日期比大小

$date1 = '2023-10-01';
$date2 = '2023-10-02';

if (strtotime($date1) < strtotime($date2)) {
    echo "$date1 is earlier than $date2";
} else {
    echo "$date1 is not earlier than $date2";
}

$date1 = new DateTime('2023-10-01');
$date2 = new DateTime('2023-10-02');

if ($date1 < $date2) {
    echo "$date1 is earlier than $date2";
} else {
    echo "$date1 is not earlier than $date2";
}

$dateString = '2023/10/01'; // 错误的日期格式
$date = DateTime::createFromFormat('Y-m-d', $dateString);

if (!$date) {
    echo "Invalid date format";
} else {
    // 正确的日期格式
    $date = new DateTime($dateString);
}

$date1 = new DateTime('2023-10-01', new DateTimeZone('UTC'));
$date2 = new DateTime('2023-10-02', new DateTimeZone('America/New_York'));

$date2->setTimezone(new DateTimeZone('UTC'));

if ($date1 < $date2) {
    echo "$date1 is earlier than $date2";
} else {
    echo "$date1 is not earlier than $date2";
}