preg_match: check birthday format (dd/mm/yyyy)

Question

How do I make the expression which checks the birthday input to match a format like this dd/mm/yyyy? Below is what I came out so far, but it takes this too if I put 99/99/9999!

if (!preg_match("/[0-9]{2}\/[0-9]{2}\/[0-9]{4}/", $cnt_birthday))
  {
   $error = true;
   echo '<error elementid="cnt_birthday" message="BIRTHDAY - Only this birthday format - dd/mm/yyyy - is accepted."/>';
  }

How can I make sure that its only 01 to 31 for dd and 01 to 12 for mm? but I am sure how to restrict yyyy... I think theoritical 9999 should be acceptable... let me know if you have a better idea!

thanks, Lau

Answer 1

I would suggest using checkdate() for this instead:

if (preg_match("/([0-9]{2})\/([0-9]{2})\/([0-9]{4})/", $cnt_birthday, $matches)) {
    if (!checkdate($matches[2], $matches[1], $matches[3])) {
        $error = true;
        echo '<error elementid="cnt_birthday" message="BIRTHDAY - Please enter a valid date in the format - dd/mm/yyyy"/>';
    }
} else {
    $error = true;
    echo '<error elementid="cnt_birthday" message="BIRTHDAY - Only this birthday format - dd/mm/yyyy - is accepted."/>';
}

So regexp validates the format, checkdate validates the actual date.

Answer 2

Based on Tim's checkdate based solution:

The extraction of day, month and year can easily be done using explode as:

list($dd,$mm,$yyyy) = explode('/',$cnt_birthday);
if (!checkdate($mm,$dd,$yyyy)) {
        $error = true;
}