Bug #2829

Possible bug in Wt::WDateTime

Added by Eivind Midtgård over 8 years ago. Updated about 2 years ago.

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The function Wt::WDateTime::currentDateTime().toLocalTime().toString() seems to return the server time, no matter what locale I set.

I do this in the application object constructor:

Wt::log("notice") << "Server time (UTC) is " << Wt::WDateTime::currentDateTime().toString();

Wt::log("notice") << "Server time (local) is " << Wt::WDateTime::currentDateTime().toLocalTime().toString();

Wt::log("notice") << "Current locale is " << Wt::WLocale::currentLocale().name();

Wt::log("notice") << "Application locale is " << locale().name();

It prints

[2014-Mar-19 17:37:54.365412] 5992 [/ sAbCaewpUIhd7zDH] [notice] "Server time (UTC) is Wed Mar 19 16:37:54 2014"

[2014-Mar-19 17:37:54.378413] 5992 [/ sAbCaewpUIhd7zDH] [notice] "Server time (local) is 2014-03-19 16:37:54"

[2014-Mar-19 17:37:54.393414] 5992 [/ sAbCaewpUIhd7zDH] [notice] "Current locale is nb-NO"

[2014-Mar-19 17:37:54.407415] 5992 [/ sAbCaewpUIhd7zDH] [notice] "Application locale is nb-NO"

I am at UTC+1. I have tried calling Wt::WEnvironment.timeZoneOffset(), and it returns 60. Application.locale().timeZone() returns an empty string.

I have tried with just the default locale, and also with calling setLocale("nb-NO"), setLocale("el-GR"), setLocale("ru-RU"), setLocale("C").

I noticed that the 'heading' from the log contains the correct time. It appears that it is implemented using some boost function.

I really would like my local time to be correct ;). What am I doing wrong?


Updated by Koen Deforche over 8 years ago

  • Status changed from New to Feedback


Instead of:


You should use:


WDateTime::toLocalTime() needs detailed locale information to convert a time to local time, whereas WLocalDateTime::currentDateTime() can use the 'current' time offset as passed by the user to convert the local time.

Note that simply using setLocale("nb-NO") only affects language, but not other locale settings (yet; we currently reconsidering if we should adopt std::locale; but currently we avoided it as it's a bug-ridden beast and a tough dependency on many embedded systems, and even if we would it would not help us with time zones since that's not a standardized facet). To set the timezone information needed for your conversion to work, you need to use app->locale().setTimeZone() using a POSIX time zone specification.

See also:

We also have a small feature example that shows how to configure the timezone from a drop-down box, which is seeded with information from the browser:

(Somehow there is no nice website that translates 'Olson' time zone names into posix time zone strings).




Updated by Eivind Midtgård over 8 years ago

Hi Koen,

Thanks, this helps. My needs at the moment are so simple that I can get by by adding the time zone offset to the UTC time.




Updated by Stefan Bn over 2 years ago

This feedback helped for me as well!

This will crash my software immediately:

WDateTime::currentDateTime().toString("dd.MM.yyyy hh:mm:ss");

while this works:

WLocalDateTime::currentDateTime().toString("dd.MM.yyyy hh:mm:ss");

I can see the difference behind it, but the former statement should at least be safe and not crashing!


Updated by Roel Standaert over 2 years ago

What? That should not cause a crash (and it doesn't when I test it).


Updated by Stefan Bn about 2 years ago

I just came across this at a point where I use WLocalDateTime inside a derived WResource class without any localization references (Wt 4.3.1 using MinGW 9.3.1 on Windows).

This crashes immediately:

WLocalDateTime::currentDateTime().toString("yyyy MMMM dd");

at the return statement in line 64 in WLocalDateTime.C

  template<class Duration>
  date::local_time<typename std::common_type<Duration, std::chrono::minutes>::type>
  to_local(date::sys_time<Duration> tp) const
    using namespace date;
    using namespace std;
    using namespace std::chrono;
    using LT = local_time<typename common_type<Duration, minutes>::type>;
    return LT{(tp + offset_).time_since_epoch()};

while this works: WDateTime::currentDateTime().toString("dd.MM.yyyy hh:mm:ss");

Also see this thread:


Updated by Stefan Bn about 2 years ago

I have a different project and the same behavior as posted before:

This crashes immediately:

WLocalDateTime now = WLocalDateTime::currentDateTime().toString();

when used in a worker thread in a WObject derived class outside a WApplication. In my previous post it happend inside a WResource. Maybe the cause is that it is called outside a WApplication?

now.isValid() returns true, but subsequent .toString() crashes.

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