How to set timezone in Qt?

Question

Can someone show me how to set time zone in Qt? Currently I am using the linux system() call to set the time zone, but this is not reflecting in currentTime() API of Qt. There is a setTimeZone() API in Qt 5 and above but I have no idea how to use it. Thanks in advance.

I don't understand what you want to achieve. Do you want to display times in the system timezone, or do you want to actually change the timezone of the system? — Frank Osterfeld, May 01 '15 at 11:24
There's no API for that in Qt. That's system configuration, usually nothing a normal application is (or should be) concerned with. — Frank Osterfeld, May 01 '15 at 13:09
what about the QDateTine::setTimeZone() API? What does it do? — jxgn, May 01 '15 at 17:38
It's sets the timezone for that particular QDateTime object, representing a date and time. It has nothing to do with the system timezone. — Frank Osterfeld, May 01 '15 at 17:44

score 1 · Answer 1 · answered Sep 24 '19 at 06:46

As stated by Frank in the comments, there is no API in Qt to directly change the system timezone. Using timedatectl is one way to go.

However instead of a system() call, QProcess could be used like this for an example timezone:

auto timezone = QString("Europe/Paris");
auto command = QString("timedatectl set-timezone ") + timezone;
auto ret = QProcess::execute(command);
if (ret != 0) {
    qDebug("timedatectl failed : %d", ret);
}

If there is already a QTimeZone object in use, the command can be assembled like this:

auto timezoneObj = QTimeZone();

// process timezoneObj

if (!timezoneObj.isValid()) {
    qDebug("invalid timezone qobject");
    return;
}

auto timezone = timezoneObj.id();
auto command = QString("timedatectl set-timezone ") + timezone;
auto ret = QProcess::execute(command);
if (ret != 0) {
    qDebug("timedatectl failed : %d", ret);
}

score 1 · Answer 2 · answered Dec 10 '19 at 17:00

Instead of using QProcess I'd probably recommend to use QDBus instead.

qdbus command line call:

qdbus --system org.freedesktop.timedate1 /org/freedesktop/timedate1 org.freedesktop.timedate1.SetTimezone Europe/Berlin false

Qt code:

QDBusInterface timedated("org.freedesktop.timedate1", "/org/freedesktop/timedate1", "org.freedesktop.timedate1", QDBusConnection::systemBus());
QDBusPendingReply<> setTz = timedated.callWithArgumentList(QDBus::Block, "SetTimeZone", {"Europe/Berlin", false});

How to set timezone in Qt?

2 Answers2