Low performance, timer and label.

[Loc888]

Hi, i have some problems with QTimer, and label. I wanna create a simple stopwatch, but the time is highly delayed, it's around 15% different, so 30s is equal to 35s.

Settext function is causing all the problems, and i need it to update the Ms label.

I am having a lot of bugs with QT, and one of them is it, i have two stopwatches, and one of them was working almost good (Very small percent of delay,almost 0), and the second one, was almost 35% of delay, horrible score.... The second one, is working on the same simple function, and i made it (It's a copy, with different variable name's).

I was trying to find the issue, why one of the timer, working with a copy of function, was doing that.
What's funny? When i just deleted the old TabWidget, and created new one (In general, i dont change any settings), now these two timers have the same delay of around 7-10%. I have no idea what's going on, and i have enough.

If you can do something, cuz i have some bugs with my Qt, sometimes when i delete some objects, then when i press one button, the application crash, and i need to delete, and rebuild the project (It doesn't work if i just press the rebuild button, i lose a lot of time before i notice that).

Release version is a completely mess up, simple calculations are giving some totally unknown results, basicly 100% is broken, functions are giving stuff from nowhere.

If i switch to debug version, everything works good. Just the timers still have that low performance.

I dont know if i should download newer version, and what is causing these problems.

[J.Hilk]

hi @Loc888 ,

from what I read, you have a real mess at your hand ;-)

Ok let us is break it down a bit

I am having a lot of bugs with QT, and one of them is it, i have two stopwatches, and one of them was working almost good (Very small percent of delay,almost 0), and the second one, was almost 35% of delay, horrible score.... The second one, is working on the same simple function, and i made it (It's a copy, with different variable name's).

Why don't you take your working StopWatch and move it into its own class? That why you can make 2 instances of the same base class/object that should behave always the same.

Release version is a completely mess up, simple calculations are giving some totally unknown results, basicly 100% is broken, functions are giving stuff from nowhere.

You need to initialize your variables the debug compiler initializes everything with 0, if you don't do it. The release one just takes what happens to be in the memory.

[Loc888]

@J.Hilk I don't understand what you mean. The problem is with settext function now, when i use it, it's delays the time.

[VRonin]

@Loc888 said in Low performance, timer and label.:

I am having a lot of bugs with Qt

Don't blame the framework. We all did it at least once. It was never the framework's fault.

Can you post your current code?

[Loc888]

@VRonin Give me back my wasted time, and i forgive him.

[VRonin]

@Loc888 said in Low performance, timer and label.:

Give me back my wasted time

I could say the same here.

If you want help, a bit of humility and accepting the fact that there's a 99.9% chance the problem is in your code and not in Qt is a first step

[Loc888]

@VRonin Ther is nothing to post, simple Qtimer and settext function. That's it.
The timer refire the function, and set the current time.

[VRonin]

Can you try this basic example?

#include <QApplication>
#include <QTimer>
#include <QLabel>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QLabel mainWid;
    QTimer mainTimer;
    int counter = 0;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid,&counter]()->void{
        mainWid.setText(QObject::tr("%1 sec").arg(++counter));
    });
    mainTimer.start(1000);
    mainWid.show();
    return a.exec();
}

[Loc888]

@VRonin It says no matching function.

[VRonin]

@Loc888 I tested it on my machine Qt 5.10 MSVC2013 x64 Win7. What version of Qt are you running?

[Loc888]

@VRonin Desktop Qt 5.2.0 MinGW 32bit

[VRonin]

Then everything should work, you probably just have to enable C++11

• add CONFIG += c++11 in your .pro file
• re-run qmake

[Loc888]

@VRonin It's working, but i need it in MS. It happens because text need to be updated fast, and it cause the problem. If i just run the timer, it's look's fine, but i need to show the time in label..

[J.Hilk]

@Loc888 I think you need to be a bit more specific, with what is going on.

It's working, but i need it in MS. It happens because text need to be updated fast, and it cause the problem. If i just run the timer, it's look's fine, but i need to show the time in label..

Updating a QLabel's text shouldn't take seconds to update

to modify the code of @VRonin abit to display time and fast changes:

#include <QApplication>
#include <QTimer>
#include <QLabel>
#include <QTime>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel mainWid;
    QTimer mainTimer;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid]()->void{
       mainWid.setText(QTime::currentTime().toString("hh.mm.ss.zz"));
    });
    mainTimer.start(10);
    mainWid.show();

    return a.exec();
}

[Loc888]

@J.Hilk I would like to use that, but i don't want current time, i want everything starting from 0.

[J.Hilk]

@Loc888
this code examples are for the purpose of trouble shooting.
But it's easy enought to adapt.

#include <QApplication>
#include <QTimer>
#include <QLabel>
#include <QTime>
#include <QElapsedTimer>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel mainWid;
    QTimer mainTimer;
    QTime time(0,0);
    QElapsedTimer actualTimePassed;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid, &time, &actualTimePassed]()->void{
        time = time.addMSecs(actualTimePassed.elapsed());
        actualTimePassed.start();
        mainWid.setText(time.toString("hh.mm.ss.zzz"));
    });
    actualTimePassed.start();
    mainTimer.start(10);
    mainWid.show();

    return a.exec();
}

[VRonin]

@Loc888 said in Low performance, timer and label.:

it's working, but i need it in MS

Unfortunately this is platform dependant. Best you could do is:

#include <QApplication>
#include <QTimer>
#include <QLabel>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QLabel mainWid;
    QTimer mainTimer;
    mainTimer.setTimerType(Qt::PreciseTimer);
    unsigned int counter = 0;
    QObject::connect(&mainTimer,&QTimer::timeout,[&mainWid,&counter]()->void{
        mainWid.setText(QObject::tr("%1 msec").arg(++counter));
        mainWid.repaint();
    });
    mainTimer.start(1);
    mainWid.show();
    return a.exec();
}

Please note, from http://doc.qt.io/qt-5/qt.html#TimerType-enum:

Precise timers try to keep millisecond accuracy

try != will, unfortunately

[Loc888]

@VRonin Maybe i expressed wrong, but i don't want it in Ms (the total), so 5500 = 5,5s, i want that pattern "mm.ss.zzz" or "mm.ss.zz" , but i want it to start from 0, not from the current time. Is any way to force it? (In sec, ther is no delay when the method update the text).

[Loc888]

@J.Hilk Guys,i tried J.Hilk code,and it's not working how it should.

It doesnt help me, it's working, but if i compare the timer to my windows time, the difference is arround 10s (after 2min test), it's too mutch.

Why it's happening?

Ps. I tried with "setTimerType(Qt::PreciseTimer);", but still doesn't help...

????????

[mpergand]

My turn ;)

QLabel label;
label.setGeometry(100,100,200,50);
 QTimer timer;
 QTime time;

 QObject::connect(&timer,&QTimer::timeout,[&time,&label](){
    QTime elapsed=QTime::fromMSecsSinceStartOfDay(time.elapsed());
    label.setText(elapsed.toString("mm:ss:zzz"));
    });

time.start();
timer.start(100);
label.show();