Include header main window to a child window in QT

Question

I try to include header window into his child window. Let see a code:

//header of main window
#include "second_window.h" // include child window

class mainclass : public QMainWindow
{
    Q_OBJECT

public:
    mainclass(QWidget *parent = 0);
    ~mainclass();
    second_window *h_secondwindow = nullptr;

private:
    Ui::mainclass ui;

};

And Second

//header second_window.h
#include "mainwindow.h" // only this from mainwindow class
class second_window : public QWidget
{
    Q_OBJECT

public:
    third_window * h_third_window = nullptr;
    second_window(QWidget *parent = 0);
    ~second_window();

private:
    void reDrawTable();
    Ui::second_window ui;

};

#endif // second_window_H

And when in "second_window.h" i try to include "header of main window" (lets call it mainwindow.h )

I got error by this line (in main window) :

second_window *h_secondwindow = nullptr;

Errors like:

//qdatetime.h ( i dont edit this file ;0 )

error C2059: syntax error : '::'
static inline qint64 nullJd() { return std::numeric_limits<qint64>::min(); }

//mainwindow.h

error C2143: syntax error : missing ';' before '*'
second_window *h_secondwindow = nullptr;

I need this variable bcoz i have to operate in main window method on this child window.

Any idea?

Answer 1

Try, cross checking your "second_window.h" to see if there any code errors, it might be there are some few errors. Such errors mainly happen with pointers and references, so an error might be possible!

Answer 2

You shouldn't include the header files inside each other. You can use a forward declaration of mainwindow class in second_window.h :

//header second_window.h
class mainwindow;

Forward declarations mean that you can only use that class as a pointer in the header file and not a class instance. So using this way you can now have a pointer to your mainwindow in second_window.h .

But it is recommended to check if you can change your design and eliminate this circular dependency.

Answer 3

I think your code is dark means. Why does second_window include main_window? You should init in main window.h:

second_window* _secondWindowUi;

in .cpp file : _secondWindowUI = new second_window(); It is easy!