how to restart my own qt application? - c++

Question

i just asking myself how to restart my own qt application?
Can somebody please show me an example?

Answer 1

To restart application, try:
#include <QApplication>
#include <QProcess>
...
// restart:
qApp->quit();
QProcess::startDetached(qApp->arguments()[0], qApp->arguments());

Answer 2

I'm taking the other answers solutions, but better. No need for pointers, but there is a need for a ; after the while statement of a do { ... } while( ... ); construct.
int main(int argc, char *argv[])
{
const int RESTART_CODE = 1000;
do
{
QApplication app(argc, argv);
MainWindow main_window(app);
} while( app.exec() == RESTART_CODE);
return return_from_event_loop_code;
}

Answer 3

Assuming that 1337 is your restart code:
main.cxx
int main(int argc, char * argv[])
{
int result = 0;
do
{
QCoreApplication coreapp(argc, argv);
MyClass myObj;
result = coreapp.exec();
} while( result == 1337 );
return result;
}
myClass.cxx
qApp->exit(1337);

Answer 4

To restart a running Qt application (at least in Qt 5.15.2) you can do the following:
#include <QApplication>
#include <QProcess>
//...
QString program = qApp->arguments()[0];
QStringList arguments = qApp->arguments().mid(1); // remove the 1st argument - the program name
qApp->quit();
QProcess::startDetached(program, arguments);

Answer 5

Doing a real process restart without subclassing:
QCoreApplication a(argc, argv);
int returncode = a.exec();
if (returncode == -1)
{
QProcess* proc = new QProcess();
proc->start(QCoreApplication::applicationFilePath());
}
return returncode;
Edit for Mac OS like earlier example.
To restart call
QCoreApplication::exit(-1);
somewhere in your code.

Answer 6

Take a look at How to restart an application thread on qtcentre.org, where muisei gives this code
#define RESTART_CODE 1000
int main(int argc, char *argv[])
{
int return_from_event_loop_code;
QPointer<QApplication> app;
QPointer<MainWindow> main_window;
do
{
if(app) delete app;
if(main_window) delete main_window;
app = new QApplication(argc, argv);
main_window = new MainWindow(app);
return_from_event_loop_code = app->exec();
}
while(return_from_event_loop_code==RESTART_CODE)
return return_from_event_loop_code;
}

Answer 7

I just used the method described above and I noticed that my application crashes on restart.
...then I switched the following lines of code:
if(app) delete app;
if(main_window) delete main_window;
to:
if(main_window) delete main_window;
if(app) delete app;
and it behaves OK. For some reason the window must be deleted first.
Just a note for future readers.
EDIT: ...and a different approach for those who want a real process-restart: You can declare a myApp::Restart() method in your subclass of QApplication. The following version works OK on both MS-Windows & MacOS:
// Restart Application
void myApp::Restart(bool Abort)
{
// Spawn a new instance of myApplication:
QProcess proc;
#ifdef Q_OS_WIN
proc.start(this->applicationFilePath());
#endif
#ifdef Q_OS_MAC
// In Mac OS the full path of aplication binary is:
// <base-path>/myApp.app/Contents/MacOS/myApp
QStringList args;
args << (this->applicationDirPath() + "/../../../myApp.app");
proc.start("open", args);
#endif
// Terminate current instance:
if (Abort) // Abort Application process (exit immediattely)
::exit(0);
else
this->exit(0); // Exit gracefully by terminating the myApp instance
}

Answer 8

This slight variation on Rubenvb's idea works with PyQt. clearSettings is the method that triggers the restart.
class GuiMain
#Most of implementation missing
def clearSettings(self):
#Clearing the settings missing
QApplication.exit(GuiMain.restart_code)
restart_code = 1000
#staticmethod
def application_main():
"""
The application's main function.
Create application and main window and run them.
"""
while True:
app = QApplication(sys.argv)
window = GuiMain()
window.show()
ret = app.exec_()
if ret != GuiMain.restart_code:
break
del window
del app

Answer 9

Here is the code:
main.cpp:
int main(int argc, char *argv[])
{
int currentExitCode = 0;
do {
QApplication a(argc, argv);
MainWindow w;
w.show();
currentExitCode = a.exec();
} while( currentExitCode == MainWindow::EXIT_CODE_REBOOT );
return currentExitCode;
}
mainwindow.h
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
static int const EXIT_CODE_REBOOT;//THIS IS THE IMPORTANT THING TO ADD TO YOUR CODE
~MainWindow();
private slots:
void slotReboot();//AND THIS ALSO
//ALL THE OTHER VARIABLES
}
The slotReboot() is the slot that will receive the signal of the QAction I'm going to show in the mainwindow.cpp
mainwindow.cpp
First initialize EXIT_CODE_REBOOT :
int const MainWindow::EXIT_CODE_REBOOT = -123456789;
and declare a QAction pointer:
QAction* actionReboot;
then in the MainWindow constructor:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
actionReboot = new QAction( this );
actionReboot->setText( tr("Restart") );
actionReboot->setStatusTip( tr("Restarts the application") );
connect( actionReboot, SIGNAL (triggered()),this, SLOT (slotReboot()));
}
And finally you need to send the signal (in the part of your code you need), in this way:
actionReboot->trigger();
I did the code I showed following these instructions: How to make an application restartable - Qt Wiki

Answer 10

You can use my open source library:
https://marketplace.qt.io/products/main-loop-wdt-for-qt-qml
It's a watchdog timer for the main qt loop, but I have a function for forced reboot, with different strategies: startdetached + exit, exec system call on Linux / macOS, and delayed restart (for example, exit and restart after 3 seconds)