Qt ISODate formatted date/time including timezone

Question

Does anyone know of a cleaner way to get the time zone included in the ISO string representation of a QDateTime?

I should be able to just use the following:

qDebug() << QDateTime::currentDateTime().toString(Qt::ISODate);

but this always comes out in UTC format:

2014-02-24T01:29:00Z

Currently, the way I'm working round this is to force the TimeSpec to be Qt::offsetFromUtc by explicitly setting the offset, which I'm getting from the QDateTime originally.

QDateTime now = QDateTime::currentDateTime();
int offset = now.offsetFromUtc();
now.setOffsetFromUtc(offset);
qDebug() << now.toString(Qt::ISODate);

This gives what was originally expected:

2014-02-24T01:29:00+02:00

Does anyone know how to do this in a cleaner way or must this be logged as a bug?

EDIT: I'm using Qt5.2.1

UPDATE:

The following small program shows what I mean:

#include <QtCore/QDateTime>
#include <QtCore/QDebug>

int main(int argc, int argv){
    qDebug() << QDateTime::currentDateTime().toString(Qt::ISODate);
    qDebug() << QDateTime::currentDateTime().toTimeSpec(Qt::OffsetFromUTC).toString(Qt::ISODate);

    QDateTime now = QDateTime::currentDateTime();
    int offset = now.offsetFromUtc();
    now.setOffsetFromUtc(offset);
    qDebug() << now.toString(Qt::ISODate);

    return 0;
}

The following output is generated:

"2014-02-24T10:20:49" 
"2014-02-24T08:20:49Z" 
"2014-02-24T10:20:49+02:00"

The last line is the one that is expected. Please note that the second time has been converted to UTC, which is not what is wanted.

Answer 1

This had not been present before 5.2, but it was integrated in there. It seems that you got the syntax incorrect though because it should be like this:

QDateTime::currentDateTime().toTimeSpec(Qt::OffsetFromUTC).toString(Qt::ISODate)

as per the corresponding bugreport. Note that toTimeSpec(Qt::OffsetFromUTC) call in the middle.

Answer 2

When I need that I use the following workaround:

QDateTime::currentDateTime().toOffsetFromUtc(QDateTime::currentDateTime().offsetFromUtc()).toString(Qt::ISODate);

I have not tested if @lpappa is working on new versions. The above workaround has been tested on Qt 5.3

Answer 3

This seems to work, with millisecond accuracy and preservation of timezone information:

#include <QDebug>
#include <QTimeZone>

QString datetimeToIsoMs(const QDateTime& dt)
{
    // An ISO-8601 format preserving millisecond accuracy and timezone.
    // Equivalent in moment.js: thing.format("YYYY-MM-DDTHH:mm:ss.SSSZ")
    // Example: '2016-06-02T10:04:03.588+01:00'
    // Here we also allow 'Z' for UTC.

    // In Qt, BEWARE:
    //      dt;  // QDateTime(2016-06-02 10:28:06.708 BST Qt::TimeSpec(LocalTime))
    //      dt.toString(Qt::ISODate);  // "2016-06-02T10:28:06" -- DROPS timezone
    QString localtime = dt.toString("yyyy-MM-ddTHH:mm:ss.zzz");
    int offsetFromUtcSec = dt.offsetFromUtc();
    // FOR TESTING: offsetFromUtcSec = -(3600 * 2.5);
    QString tzinfo;
    if (offsetFromUtcSec == 0) {
        tzinfo = "Z";
    } else {
        QString sign = offsetFromUtcSec < 0 ? "-" : "+";
        offsetFromUtcSec = abs(offsetFromUtcSec);
        int hours = offsetFromUtcSec / 3600;
        int minutes = (offsetFromUtcSec % 3600) / 60;
        tzinfo += QString("%1%2:%3").arg(sign)
            .arg(hours, 2, 10, QChar('0'))
            .arg(minutes, 2, 10, QChar('0'));
        // http://stackoverflow.com/questions/2618414/convert-an-int-to-a-qstring-with-zero-padding-leading-zeroes
    }
    return localtime + tzinfo;
}

QString datetimeToIsoMsUtc(const QDateTime& dt)
{
    QDateTime utc_dt = dt.toTimeSpec(Qt::UTC);
    return datetimeToIsoMs(utc_dt);
}

QDateTime isoToDateTime(const QString& iso)
{
    return QDateTime::fromString(iso, Qt::ISODate);
}