access main window from function

[eric]

Hello!

How do you access the main window (that's declared only in main function) from other functions of the same class?
This below is my main() and I can resize the window as shown.

int main(int argc, char *argv[])
{
    QApplication application(argc, argv);
     MyWidget window;
    window.resize(1200,800);
    window.show();
    return application.exec();
}

int main(int argc, char *argv[])
{
    QApplication application(argc, argv);
     MyWidget window;
    window.resize(1200,800);
    window.show();
    return application.exec();
}

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But why can't I do it from another function like

void MyWidget::reSize()
{
window.resize(1200,800);
}

void MyWidget::reSize()
{
window.resize(1200,800);
}

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The comiler complains like this: "insufficient contextual information to determine type". I think I need to declare "window" somewhere else to make this work.
I do not think that I can declare "window" in my *.h file, can I? Isn't this instance a bit different from all others?