compare dates

NZ_Kiwis

I want to see if the date today is greater or equal to the date my cusomter is trying to view. this is what I have and it does not work?

$Today = time();
$Day = $_GET['Day'];
$Month = $_GET['Month'];
if ($Today >= mktime(0,0,0,$Month,$Day,2013)){
...

dalecosp

Works for me, assuming I use a hard-coded value like 2 for $Day and 11 for $Month (as it's the 3rd here now). I couldn't be arsed to create a form to submit in order to have GET set.

That said, could it be timezone issues?

sneakyimp

So I have somehow gotten by without having the full 'awakening' when it comes to comparing timestamps and dates. Dalecosp makes a very good point. Time zones matter.

For example (and this happens to me a lot), your user might be in London where it is 1:00AM on December 5th (time zone is GMT). Your server might be in Los Angeles where at that exact same moment it's 5:00PM (time zone is PST). You might need to take into account your time zone, the time zone of your server, and also the time zone of a visitor to your site (or bazillions of visitors from different time zones). I've yet to learn any hard-and-fast rules or heuristics that mitigate the problem of reckoning time zones. Looking forward to hearing any if folks have them.

You should probably read the docs on [man]time[/man], [man]mktime[/man] and [man]gmmktime[/man]

maxxd

Yeah, timezones can mess with your head.

I've tried - and had some success - with converting all times to your local timezone before comparing. The issue that you run into here is daylight savings time, which of course some areas honor and others don't. That having been said, if you instantiate a DateTimeZone() object set to the user's locale, you can instantiate a new DateTime() object using the user input and that DateTimeZone() object. Then set the timezone to GMT or your servers local timezone before doing the conversion.

private $_userTZ;

public function doCompare(){
     $this->_userTZ = new DateTimeZone(/*Get the string from a database if possible*/);
     $uDate = new DateTime($_GET['userDate'], $this->_userTZ);
     $uDate->setTimeZone('UTC');
     $compareDate = new DateTime(); //this will set the timezone to either the user or server timezone (I can't remember which, sorry...)
     $compareDate->setTimeZone('UTC');
     if($uDate >= $compareDate){
          print("<p>Yup, {$uDate->format('Y-m-d')} is greater than or equal to {$compareDate->format('Y-m-d')}</p>");
     }else{
          print("<p>Nope. {$uDate->format('Y-m-d')} is not greater than or equal or {$compareDate->format('Y-m-d')}</p>");
    }
}

Again, this is dodgy as DST is not taken into account, but has worked in the majority of situations I've used it. Of course, we also had the luxury of having all our customer's timezones stored in the customer table in the database, so that made life a bit easier as well.

Very much looking forward to other ideas on how to handle this...

sneakyimp

I have a passing familiarity with the fancy DateTimeZone and DateTime objects. My experience and instinct tell me that it's probably better to store timestamps of any as GMT in your database. Or possibly as the server's time zone (so that easy comparisons to the server's current time are possible). On the display end, it is of course always important to know the user's timezone so that you can do a conversion. I think Javascript lets you sniff out a user's timezone somehow, but don't recall the specifics.