How does PHP time() work in following case:
User is posting something in database and posting stamp is added also which is just time().
But how to compensate for time zones? What if two users from EU and USA are posting at the same time, will the posting stamp be the same?
The whole point is that the time()-method stores everything in the same timezone, the one the server is configured with.
If it did not do this, it would be impossible to know when something really happened.
If you want to display datetime with timezones, you can output the timestamp from the server, use javascript or something to calculate the clients timezone offset and add/substract hours to the time.
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I ran into trouble while dealing with date and time using php and mysql. I am trying to store local time of user's timezone as a timestamp on mysql db and would like it to convert back to normal date and time at the time of output.
This is the first time I am dealing with date and time.
As I understand: I can't rely on PHP's time() as it returns servers time according to server's timezone and the same case with mysql current_timestamp.
I can use the javascript to get user's local timezone and then can use date_default_timezone_set() for each session.
If I am doing right, now the confusion starts.
As you can understand the users will come from around the globe, so if two users (one from US and another from India) do something at the same time, will it show each others time as identical or it will show some difference? I mean it shouldn't show Indian user that the US user has done something few hours ago as the US user done at same time.
Please let me know if I don't understand these things properly.
What I want to achieve is, the output of the time should show in local time format. Ex: any time should show in IST format for Indian user and other country respectively.
Best way to achieve this is to store date in a database in a standard format (eg. GMT).
After getting user's timezone through javascript, you may convert date to user's timezone & display accordingly.
As working on a large application I am trying to make the datetime stamps reconcile with the current user time. so If activity id done at 3:00PM then the every user see it at 3:00PM
So Here is solution steps to the problem. on this and please correct me or lead me to the right direction if I am not on the right direction.
Store all datetime in MySql as UTC time.
Store time zones in a table with the current offset. for example
zone_id zone_name utc-offset
1 Central -6
In my users table I have a field for user_time_zone_id and in that field I will have the value "1" in the user setting so it will say that this user is using the system from "Central" location.
In my php application configuration I set the default time zone to UTC like this
date_default_timezone_set('UTC');
Once I load this application I define the user offset and on each datetime out put I do the calculation of the time. for example date('Y-m-d', strtotime($current_offset.' hour')) where $current_offset = -6 as it is define by the user profile upon the page load.
Here are my questions.
Is my approach to this problem correct?
Is there a better way of doing this?
How to calculate the daylight saving time? Please keep in mind that there are some parts of the country that does not have daylight saving.
I had a similar thing one time, and it ended up being a pain to try to keep track of users timezones and daylight savings, especially when half your clients are in AZ which doesn't have daylight savings. I don't know if this is possible for you, but what I ended up doing was just store everything in UTC and then used JS to convert it to the users local time with the Date object. It was done through an ajax call, but you could also echo a document.write if you needed to.
You shouldn't need to use date_default_timezone_set, use the PHP DateTime class which has native support for timezones. Or, like #romo says, you can do it on the client in JavaScript.
Well I know that this question may be asked many times but certainly I've few doubts In my mind, and by the way don't comment that what I've tried, I've tried many ways but am just asking what's the correct and easier way as there are many posts lingering out here with different suggestions for accomplishing these tasks, so I'll explode() my question into smaller questions...
So can you people just guide me where am going right or wrong as am sure many people are confused when it comes to date/time
1) Why/how to save time as UTC in MySQL using PHP?
Personally for this I post this using php $year/$month/$day and check the date using checkdate() in mysql date field. so is it ok or should I use timestamp and than explode the retrieved string on front end using php?
2) If I run server from India, should I record default time using date_default_timezone_set("Asia/Calcutta"); and than subtract and add time using php function or while posting only I should check users time zone selected from his user accound and accordingly set a condition kinda:
if(timezoneselected == +5.30) {
echo date_default_timezone_set("Asia/Calcutta");
} elseif(timezoneselected == +anytime) {
echo another country timezone
}
3) last question is how websites like gmail facebook etc manages time? I mean if they are saving datetime according to their server than how they show perfect posted time for each user, even gmail, if I send a mail to another user, my sent time and the person living in another country gets email at his printed local time I mean how we can do this, sorry am not able to explain you perfectly say this example,
facebook:
user from India posts, facebook shows posted 8 mins ago, 9mins ago, fine after sometime they show a real date, and that date is perfect according to the time I posted, however if a person from USA updates, say 8 mins ago 9mins ago on his profile but his original posted time is shown correctly to him, and even correctly to me?
sorry for this question but really this will help me understanding this date/time concept and will also be helpful to future users. Thank you!
Bottom line, you should store everything UTC
When you display times for a particular user, use a timezone of their choosing. Store the timezone of the user, like "Asia/Calcutta" and simply convert the time when displaying it using the date_default_timezone_set method.
I will attempt to answer your questions from the comment here.
You store everything UTC always. It is the baseline. When you display the times associated with anything you convert based on the user. If you want to display Posted 8 mins ago then you are taking the delta between the current UTC time and the UTC time associated with a post. If you send a message from user A (in India) to user B (in Los Angeles, USA) then you would store the message time in UTC. If user A is viewing it, the time would be converted to "Asia/Calcutta" and if user B is viewing it, the time would be converted to "America/Los_Angeles". Using UTC will make your life a lot easier. Trust me.
As described in MySQL Server Time Zone Support:
The current session time zone setting affects display and storage of time values that are zone-sensitive. This includes the values displayed by functions such as NOW() or CURTIME(), and values stored in and retrieved from TIMESTAMP columns. Values for TIMESTAMP columns are converted from the current time zone to UTC for storage, and from UTC to the current time zone for retrieval.
Therefore, if you use TIMESTAMP type columns, MySQL will handle timezone conversion for you automatically: just set the appropriate timezone for the session in its time_zone variable.
I have a table of 'notifications' which may or may not be sent in any 24 hour period. Each notification has it's own timezone offset from GMT, so I have a column for offset which will be +/- in seconds.
I need to create a PHP script which will regularly (via cron) check the database for sent notifications, and then reset them to unsent if their time has passed 00:00 for that day. I'm really struggling with the best way to do this - is there a simple calculation I can make?
I was thinking of something around getting the UNIX time for the server's midnight using mktime() [my server is in GMT], and working it out with the offset in seconds, but every way I think of seems wrong.
Something like:
if(!mktime()-$notifcationTimezone > $serverMidnight){}
I'm not saying this doesn't work, but I don't think it will work when the server elapses into another day. It just confuses me, and I have no faith in it.
Isnt this just a simple comparison with strtotime and you dont even need to add up the offset. You can use the date function to set a specific time you want to pass to the strtotime which you want to use to compaire against.
To give us a better idea show us a real example from you database and what the cron looks like right now.
I'm not totaly sure what you are trying to pull of here but, what you might wanna think about is do you really want to reset anything, is it needed? You could fill in at what date your notification got send. If it does not match the date of today you want to resend it again?
I have a social network site I have been working on for a couple years in PHP/MySQL, I am now re-buidling the whole site from scratch again though. This time around I would really like to add in the ability for users to set a timezone for times on my site.
So with that said, I am asking on a guide from start to finish of the steps I need to include to do this please. My old site used mysql datetime for all dates and times and it worked great but I read that it is best to use like a text filed and store all dates and times with UTC, can someone explain how I could do this? Would I still be able to use the now() function in php to save a time to the mysql?
Also I have seen the list that php can generate of all the timezones, the one where it shows like a million (not really) but I am wondering, would it be possible to show some sort of map with images or something and link to the main timezones?
Please any tips for setting a users timezone, I can do that part, but once I have a user's timezone saved and ready to use, how can I make sure the users see's the correct time and how do I save times in the correct time.
Sorry if this was confusing, any help would be great though, thanks.
When working with php, from my experience, it is the best to store timestamps, generated with time(), as an int in the database. While it may not be that easy to read them when looking at the database (as you cannot guess the actual date just from the number), but the timestamp is the most-native thing when working with dates in php.
To save each user's timezone, you can simply save the offset, in either hours, or better (as some timezones are half an hour off) in minutes. So for example my timezone offset would be +60 (UTC+1), while in America most will have something like -480 (UTC-8) or similar.
Then when displaying the times for a user, you just pick the timestamp (which is in UTC time) and the timezone offset and generate a readable date from it using the standard date() function for formatting.
For example:
<?php
$time = time(); // from database or time() for "now"
$offset = -480; // from database
// add the offset to the time you want to display and you have the user's time
echo date( 'd.m.Y H:i', $time + $offset * 60 );
?>
In addition you could then also store the formatting string (d.m.Y H:i) in the database, so that every user can pick his favorite format.
This topic gets complicated especially when you factor in daylight savings and the fact that your server will be in a different time zone from some of your members.
I suggest you take a look at some libraries out there that have been built to handle these issues. The PEAR package Date might be a good place to start. http://pear.php.net/package/Date
Basically, you would want your members to select a timezone for their profile. Then convert all times to UTC (to remove the offset of the server location) and store them in your database as a timestamp. When displaying the times, apply the timezone offset the member chose for themself (maybe with UTC as the default) as well as a date display format.