php check for a valid date, weird date conversions

Question

Is there a way to check to see if a date/time is valid you would think these would be easy to check:

$date = '0000-00-00';
$time = '00:00:00';
$dateTime = $date . ' ' . $time;

if(strtotime($dateTime)) {
    // why is this valid?
}

what really gets me is this:

echo date('Y-m-d', strtotime($date));

results in: "1999-11-30",

huh? i went from 0000-00-00 to 1999-11-30 ???

I know i could do comparison to see if the date is either of those values is equal to the date i have but it isn't a very robust way to check. Is there a good way to check to see if i have a valid date? Anyone have a good function to check this?

Edit: People are asking what i'm running: Running PHP 5.2.5 (cli) (built: Jul 23 2008 11:32:27) on Linux localhost 2.6.18-53.1.14.el5 #1 SMP Wed Mar 5 11:36:49 EST 2008 i686 i686 i386 GNU/Linux

Answer 1

echo date('Y-m-d', strtotime($date));

results in: "1999-11-30"

The result of strtotime is 943920000 - this is the number of seconds, roughly, between the Unix epoch (base from which time is measured) to 1999-11-30.

There is a documented mysql bug on mktime(), localtime(), strtotime() all returning this odd value when you try a pre-epoch time (including "0000-00-00 00:00:00"). There's some debate on the linked thread as to whether this is actually a bug:

Since the time stamp is started from 1970, I don't think it supposed to work in anyways.

Below is a function that I use for converting dateTimes such as the above to a timestamp for comparisons, etc, which may be of some use to you, for dates beyond "0000-00-00 00:00:00"

/**
 * Converts strings of the format "YYYY-MM-DD HH:MM:SS" into php dates
 */
function convert_date_string($date_string)
{
    list($date, $time) = explode(" ", $date_string);
    list($hours, $minutes, $seconds) = explode(":", $time);
    list($year, $month, $day) = explode("-", $date);
    return mktime($hours, $minutes, $seconds, $month, $day, $year);
}

Answer 2

From php.net

<?php
function isValidDateTime($dateTime)
{
    if (preg_match("/^(\d{4})-(\d{2})-(\d{2}) ([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])$/", $dateTime, $matches)) {
        if (checkdate($matches[2], $matches[3], $matches[1])) {
            return true;
        }
    }

    return false;
}
?>

Answer 3

If you just want to handle a date conversion without the time for a mysql date field, you can modify this great code as I did. On my version of PHP without performing this function I get "0000-00-00" every time. Annoying.

function ConvertDateString ($DateString)

{

list($year, $month, $day) = explode("-", $DateString);

return date ("Y-m-d, mktime (0, 0, 0, $month, $day, $year));

}