subclassing MainForm class

[jacek]

How did you declare that slot? Could you also post the .pro file?

[mickey]

Hi, the error message above is at runtime (in console).
I saw now the problem is in other place...

//myWidget.h
class MyWidget {
    MainForm* w;

//myWidget.h
class MyWidget {
    MainForm* w;

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}
When I use in costructor of MyWidget: "connect(this, SIGNAL(myUpdate()), w, SLOT(myUpdateWidgets()) );" w pointer refers to MainForm;
But if I change in 'myMainForm* w' (in mywidget.h), compiler says me 'class redefinition error....' (error refers to line "class myMainForm {...." in mymainform.h)
I need a pointer to myMainForm class from MyWidget class (as It was for MainForm..)
Thanks

[jacek]

But if I change in 'myMainForm* w' (in mywidget.h), compiler says me 'class redefinition error....' (error refers to line "class myMainForm {...." in mymainform.h)

Could you at least learn to post exact error messages?

I need a pointer to myMainForm class from MyWidget class (as It was for MainForm..)

If you need that pointer only to make the connection, then make this connection in a different place (where you have both pointers).

[mickey]

Thanks. The error is:

mymainform.h(4): error C2011: 'myMainForm' : 'class' type redefinition

mymainform.h(4): error C2011: 'myMainForm' : 'class' type redefinition

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I need to obtain his pointer here.
I don't undertand why for MainForm there aren't problems (I declareed pointer to myMainForm in the same way of pointer to MainForm:

//mywidget.h
class MyWidget {
  MainForm* w;		
  myMainForm* myw; 
}

//mywidget.h
class MyWidget {
  MainForm* w;		
  myMainForm* myw; 
}

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[jacek]

mymainform.h(4): error C2011: 'myMainForm' : 'class' type redefinition

What do you have in 4th line of the mymainform.h class?

Did you guard all your headers using following code?

#ifndef __FILE_NAME_H__
#define  __FILE_NAME_H__
...
#endif // __FILE_NAME_H__

#ifndef __FILE_NAME_H__
#define  __FILE_NAME_H__
...
#endif // __FILE_NAME_H__

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[mickey]

Now compile successful.
the line 4 is:

class myMainForm : public MainForm

class myMainForm : public MainForm

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in mywidget.h I have #include "mymainform.h"
in mymainform.h I have #include "mywidget.h"
Is it a cycle!? Is this the cause?
Thanks

[jacek]

in mywidget.h I have #include "mymainform.h"
in mymainform.h I have #include "mywidget.h"
Is it a cycle!?

Yes, it is. You can avoid it using forward declaration.

[mickey]

sorry,
what does 'forward declarations' mean?

[jpn]

sorry,
what does 'forward declarations' mean?

Ever tried google?

[mickey]

Hi I tried this and work!

#ifndef MYMAINFORM_H
#define MYMAINFORM_H
//#include "mywidget.h"
class MyWidget;
 
class myMainForm : public MainForm
{
    Q_OBJECT
 
public:
    myMainForm( QWidget* parent = 0, const char* name = 0, WFlags fl = WType_TopLevel );
    ~myMainForm();
	MyWidget* myWidget2;
	MyWidget* myWidget3;
 
public slots:
	void myChangeView(QAction* action);
signals:
	void myMainFormUpdate();
};
#endif

#ifndef MYMAINFORM_H
#define MYMAINFORM_H
//#include "mywidget.h"
class MyWidget;

class myMainForm : public MainForm
{
    Q_OBJECT

public:
    myMainForm( QWidget* parent = 0, const char* name = 0, WFlags fl = WType_TopLevel );
    ~myMainForm();
	MyWidget* myWidget2;
	MyWidget* myWidget3;

public slots:
	void myChangeView(QAction* action);
signals:
	void myMainFormUpdate();
};
#endif

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A Question: to toggle include "mywidget.h" I needed to insert #include "mywidget.h" inside mymainform.cpp. Wasn't it the same? Why is better of my previus code (apart avoid cycle problem).
Thanks

[jpn]

A Question: to toggle include "mywidget.h" I needed to insert #include "mywidget.h" inside mymainform.cpp. Wasn't it the same? Why is better of my previus code (apart avoid cycle problem).
Thanks

You should use forward declarations whenever possible. Use includes only when forward declaration is not suitable.

Forward declaration is adequate for pointers and references. You have to use includes when compiler needs to know the size of a type. This is the case when you inherit from a class or you have an aggregate object as a class member variable.

By filling your header files with unnecessary includes only generates extra dependencies and slows compiling down for no purpose at all.