How to get QMainWindow position

[sh_erfan]

Hello
I am new to Qt
I have written a simple application and I want to get current position of the QMainWindow.
this is my code:

M::M(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::M)
{
    ui->setupUi(this);
    QMessageBox msg;
    msg.setText(QString::number("what returns the X or Y of the window?"));
    msg.exec();
}

M::M(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::M)
{
    ui->setupUi(this);
    QMessageBox msg;
    msg.setText(QString::number("what returns the X or Y of the window?"));
    msg.exec();
}

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I searched a lot. There where topics about setting the position, not getting it.
I also tried geometry().x(), but it always returns 0 !!!
Please help me. I need this.
Best regards...