how to close application

[mohanakrishnan]

hi
i can close the application from the main function using widget object
like below; my application having 3 files main,widget.cpp,widget.h below is main.cpp

QApplication a(argc, argv);
    Widget *w=new Widget();
    w->close();
    w->show();
    return a.exec();

QApplication a(argc, argv);
    Widget *w=new Widget();
    w->close();
    w->show();
    return a.exec();

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but im unable to close the application from the widget.cpp like below

void  Widget::read_db_settings()
{
QFile file("ncssettingss.ini");
    if(file.open(QFile::ReadOnly))
    {
    this->close();
}
}

void  Widget::read_db_settings()
{
QFile file("ncssettingss.ini");
    if(file.open(QFile::ReadOnly))
    {
    this->close();
}
}

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ie if the file is not fount then close the application ...
can any help me how to do this...
thanks in advance...