How to work with time intervals in Qt?

MrShawn

A lot of times I will use QTimer singleshot and connect the timeout signal to a slot to do a task every x ms. If i need it to repeat I start my timer again at the end of the slot's execution.

SGaist

Hi,

IIRC, there was at some point discussions about a class named QTimeSpan. You have to search for it.

Or maybe std::chrono may have what you want.

Eddy

a long time ago @Andre was working on that.

I found the thread here on the forum:
https://forum.qt.io/topic/3160/qtimespan-interest

hope it helps

JonB

@r3d9u11
TimeSpan in C# has nothing to do with clocks/timers/timeouts/signals, it's just a data type for manipulating time periods, which happens to go down to milliseconds/ticks.

If you are in C++, given @SGaist's link to std::chrono and its members like duration, it hardly seems worth worrying about/waiting for Qt to implement anything when you have that to use. If you're using Python, the language has library datetime.timedelta.

r3d9u11

@eddy Thank you, I watched this topic, too (so, this topic is just a continuing of that discussion)

r3d9u11

@sierdzio Thak you, however something wrong with QDateTime. It work incorrectly when date is zero.
For example:

#include <QCoreApplication>
#include <QDateTime>
#include <QDebug>

void print_date(const QDateTime& qdt)
{
    qDebug() << qdt.date().toString("yyyy:MM:dd") << "-" << qdt.time().toString("hh:mm:ss");
}

int main ()
{
    QDateTime qdt(QDate(0, 0, 0), QTime(0, 0, 0));
    print_date(qdt);

    qdt = qdt.addSecs(5);
    print_date(qdt);

    qdt = qdt.addMSecs(3600003);
    print_date(qdt);

    return 0;
}

will output:

"" - "00:00:00"
"" - ""
"" - ""
Press <RETURN> to close this window...

In that time, if we change date to (1,1,1) it will work fine:

...
QDateTime qdt(QDate(0, 0, 0), QTime(0, 0, 0));
...

result:

"0001:01:01" - "00:00:00"
"0001:01:01" - "00:00:05"
"0001:01:01" - "01:00:05"
Press <RETURN> to close this window...

Maybe I don't understand something ?

Tested with Qt 5.9.7 and Qt 5.12.4

r3d9u11

@jonb Hi, thak you for your notes. I'm on C++ and I don't need any related to timers,timeouts,signals. I just need to manipulate time interval. For example add milliseconds and finally get time interval on hours/minutes, or substract some seconds and finally get resulted time interval.

Well I implemented my own class QTimeSpan, it uses alot dividing opetions and remainder of the division but it is easy to use, implemented for the short time and does needed functions :D

However, QDateTime can do all these functions, but I faced with some strange but (as I noted below).

r3d9u11

@sgaist thank you fot hint. I'll read about it, I am a supporter of "standard" functions and methods (and hate to do own vechicles)

r3d9u11

Thank you all for answers and hints.

Well, finally there is 3 ways to work with time intervals in Qt/C++:

Qt-way: You can use QDateTime
C++-way: You can use std::chrono
Funny and ugly way: You can produce your own vehicle to implement functions what do you need

I think this theme can be closed.

Christian Ehrlicher

@r3d9u11 said in How to work with time intervals in Qt?:

but I was facing with some strange behavior or bugs

You simply didn't read the documentation: https://doc.qt.io/qt-5/qdate.html#QDate-2 : "Year 0 is invalid."

r3d9u11

@christian-ehrlicher you're right, I didn't do it completely (because mostly I read about QDateTime).
It seems like stick in the wheel. I hope there is some really important reasons to exclude zero from valid values.

In that case there is only two ways: clean C++ and own vehicle.

Christian Ehrlicher

@r3d9u11 said in How to work with time intervals in Qt?:

I hope there is some really important reasons to exclude zero from valid values.

Yes, read the documentation (as I said before): https://doc.qt.io/qt-5/qdate.html#remarks

r3d9u11

@christian-ehrlicher Yeah, I read it after was commenting, my bad :D
Thanks, again.

Finally I did that task with QDateTime and have got results like (example here):

"02:30:01.205"
Press <RETURN> to close this window...

or

"146:30:01.205"
Press <RETURN> to close this window...