class YourClass {

public:
  YourClass (QMainWindow mainwindow_ptr)
  {
    m_mainwindow = (unsigned int)mainwindow_ptr;
  }

private:
  unsigned int m_mainwindow_ptr;
}


 --------
when you want something, write that:
 ((QMainWindow *)this->m_mainwindow_ptr)->function_from_QMainWindow_class();

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and to create:


QMainWindow *wnd;
YourClass *y = new YourClass(wnd);