c++ - How can a QWidget get the "entire" parent? -

i have instantiated widgetclass in mainwindow.cpp. want pass in "this" widget more (qwidget* parent) (mainwindow* parent). on build, widgetclass established before mainwindow , errors out.

i want instancevariables in mainwindow??

ie:

mywidget(qwidget* parent, mainwindow* parent); 

there issues on such task.. maybe problem have use forward declaration include 1 class in 1 other include first ones.. or maybe fact default constructor of qwidget has first argument default parameter.. error exactly?

anyway, here complete example:

mainwindow.h

#ifndef mainwindow_h #define mainwindow_h  #include <qmainwindow> #include "mywidget.h"  namespace ui { class mainwindow; }  class mainwindow : public qmainwindow {     q_object  public:     explicit mainwindow(qwidget *parent = 0);     ~mainwindow();     int foo(int n); private:     ui::mainwindow *ui;      mywidget *w; };  #endif // mainwindow_h 

mainwindow.cpp

#include "mainwindow.h" #include "ui_mainwindow.h" #include <iostream> mainwindow::mainwindow(qwidget *parent) :     qmainwindow(parent),     ui(new ui::mainwindow) {     ui->setupui(this);     w = new mywidget(this);     this->setcentralwidget(w); }  mainwindow::~mainwindow() {     delete ui; }  int mainwindow::foo(int n) {     std::cout << "foo" << std::endl;     return n+42; } 

mywidget.h

#ifndef mywidget_h #define mywidget_h  #include <qwidget>  class mainwindow;  class mywidget : public qwidget {     q_object public:     explicit mywidget(mainwindow *main, qwidget *parent = 0); signals: public slots: };  #endif // mywidget_h 

mywidget.cpp

#include "mywidget.h" #include "mainwindow.h" #include <iostream>  mywidget::mywidget(mainwindow *main, qwidget *parent) :     qwidget(parent) {     std::cout << main->foo(0) << std::endl; } 

does help?