How to make StopWatch in QT c++?

Question

I'm making an app on QT with UI. Also, I have a function. I want to display the running time of a function. I also want to pause the stopwatch. Any ideas on how to properly embed a stopwatch in my application? Here is my code:

void SomeFunc()
{
while (1)
{
// Start Timer
// some code
// Stop Timer
// Start Timer2
// some code
// Stop Timer2
}
}

on_push_button()
{
auto futureWatcher = new QFutureWatcher<void>(this);
    QObject::connect(futureWatcher, &QFutureWatcher<void>::finished, futureWatcher, &QFutureWatcher<void>::deleteLater);
    auto future = QtConcurrent::run( [=]{ PackBytes( file_path, file_name, isProgressBar); });

    futureWatcher->setFuture(future);
}

I think you should use [QTimer](https://doc.qt.io/qt-5/qtimer.html) — Parisa.H.R, Apr 18 '22 at 11:12
if I use a QTimer, I will have to process the function 100 times per second via a signal. I don't think it's good. — Ростислав Романец, Apr 18 '22 at 11:32
by "stopwatch", you mean you want to track how long the computation in "PackBytes" is already running, right? by "pausing", do you mean the computation should also be stopped, or do you only want the time to stop...? — codeling, Apr 18 '22 at 11:55
You probably want [https://doc.qt.io/qt-5/qelapsedtimer.html](https://doc.qt.io/qt-5/qelapsedtimer.html) — drescherjm, Apr 18 '22 at 11:59
Does "display" in this context mean "show an animated elapsed-time value in a GUI widget while the function is executing", or does it mean "print the total time it took for the function to executed to stdout after the function has returned"? — Jeremy Friesner, Apr 18 '22 at 14:45
@JeremyFriesner I mean to show an animated elapsed-time value in a GUI widget while the function is executing — Ростислав Романец, Apr 19 '22 at 12:41
@codeling Yes, by 'stopwatch' I mean to track how long the computation in "PackBytes" is already running, and by "pausing" I mean the only stopwatch to stop — Ростислав Романец, Apr 19 '22 at 12:43
@РостиславРоманец does the provided answer solve your problem? — codeling, Apr 19 '22 at 18:20

codeling · Accepted Answer · 2022-04-19T18:21:26.167

Use QElapsedTimer for measuring the duration since starting the computation. Judging from your previous questions on very related topics, you do have a MainWindow class that contains the on_push_button function. In that class, declare the QElapsedTimer member; then start it when your computation starts.

Use a QTimer to update the GUI element you use for displaying the current duration (only needs to run once a second or so).

Example code:

in your header file:

#include <QElapsedTimer>
#include <QTimer>
//...

class MainWindow
{
    // ... other stuff you have
private:
    QTimer m_stopwatchUpdate;
    QElapsedTimer m_stopwatchElapsed;
};

in your cpp file:

void MainWindow::on_push_button()
{
    // ideally do this once only in the constructor of MainWindow:
    connect(&m_stopwatchUpdate, &QTimer::timeout, this, [=]{
        //.. update GUI elements here...
    });
    auto futureWatcher = new QFutureWatcher<void>(this);
    connect(futureWatcher, &QFutureWatcher<void>::finished, futureWatcher, &QFutureWatcher<void>::deleteLater);
    auto future = QtConcurrent::run( [=]{
        m_stopwatchElapsed.start();
        PackBytes(file_path, file_name, isProgressBar);
    });
    m_stopwatchUpdate.start(1000);
    futureWatcher->setFuture(future);
}

How to make StopWatch in QT c++?

1 Answers1