Regex to validate date in PHP using format as YYYY-MM-DD

Question

I am trying to make a date regex validator. The issue I\'m having is that I\'m using an input field with \"date\" type, which works like a charm in Chrome; it o

Answer 1

Check and validate YYYY-MM-DD date in one line statement

function isValidDate($date) {
    return preg_match("/^(\d{4})-(\d{1,2})-(\d{1,2})$/", $date, $m)
        ? checkdate(intval($m[2]), intval($m[3]), intval($m[1]))
        : false;
}

See the details in my answer here.

Don't use blindly DateTime::createFromFormat to validate dates. Let's take non-existent date 2018-02-30 and see:

$d = DateTime::createFromFormat("Y-m-d", "2018-02-30");
var_dump((bool) $d); // bool(true)

Yes, it returns true, not false as you may expected. More interesting:

$d = DateTime::createFromFormat("Y-m-d", "2018-99-99");
var_dump((bool) $d); // bool(true)

Also true... So, it validates just the number of digits. One more try:

$d = DateTime::createFromFormat("Y-m-d", "ABCD-99-99");
var_dump($d); // bool(false)

At last false.

What is going on here we can see from this snippet:

$d = DateTime::createFromFormat("Y-m-d", "2018-02-30");
var_dump($d);

// var_dump OUTPUT
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2018-03-02 16:41:34.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(3) "UTC"
}

As you can see when we pass non-existent 2018-02-30, the DateTime object contains 2018-03-02. I assume that it's because February 2018 has 28 days, i.e. the maximum date is 2018-02-28, and when we pass the day 30, createFromFormat just adds 30 days to the 2018-02-01 and create new date without any preceding date validation.