how to close application

[spirit]

another way it is to do like this

void Widget ::read_ncssettings()
{
   QFile file("ncssettingss.ini");
    if(file.open(QFile::ReadOnly))
    {
        QMessageBox::information(this, "OK !", "file found, yeppie");
        QTextStream ts(&file);
        this->portno=ts.readLine(100);
        portno=portno.trimmed();
        this->baudrate=ts.readLine(100);
        baudrate=baudrate.trimmed();
        this->fmsname=ts.readLine(100);
        fmsname=fmsname.trimmed();
        qDebug() << baudrate;
        file.close();
    }
    else //if file is not found then give msg box and close the app
    {
		QMetaObject::invokeMethod(this, "close", Qt::QueuedConnection);//important line
   }
 
}

void Widget ::read_ncssettings()
{
   QFile file("ncssettingss.ini");
    if(file.open(QFile::ReadOnly))
    {
        QMessageBox::information(this, "OK !", "file found, yeppie");
        QTextStream ts(&file);
        this->portno=ts.readLine(100);
        portno=portno.trimmed();
        this->baudrate=ts.readLine(100);
        baudrate=baudrate.trimmed();
        this->fmsname=ts.readLine(100);
        fmsname=fmsname.trimmed();
        qDebug() << baudrate;
        file.close();
    }
    else //if file is not found then give msg box and close the app
    {
		QMetaObject::invokeMethod(this, "close", Qt::QueuedConnection);//important line
   }

}

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btw, in this case you don't need to use setQuitOnLastWindowClosed at all.
so, the main should look like.

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}

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