Peculiar problem with QUndoCommand in a new class files.

TheCrowKaka

Hello,

I have a project that was originally created in Qt 5.5 or older version. I have implemented the Undo/Redo Framework and that works like a charm.

However, i am facing a peculiar problem that i am unable to understand the reason.

At present I have around 15 files where different classes subclassing the QUndoCommand are created and working.
Say for example, the file abc1.h and abc1.c where 2 classes subclassing the QUndoCommand are defined.

The problem happens when i create a new class header and c file and define a class subclassing the QUndoCommand.
Say for example, i create a file modifyprop.h and modifyprop.c and define the subclass of QUndoCommand. Giving here the typical class.
Header file modifypropcmd.h is as follows:

#ifndef MODIFYPROPCMD_H
#define MODIFYPROPCMD_H

#include <QUndoCommand>
#include "basegraphicentity.h"
#include "mymainview.h"

class modifypropcmd: public QUndoCommand
{
public:
    modifypropcmd(mymainview *thisview, baseblockentity *item,QUndoCommand *parent = 0);

    void undo();
    void redo();

private:
    mymainview *myGraphview;
    baseblockentity *myitem;

};

#endif // MODIFYPROPCMD_H

The CPP File "modifypropcmd.cpp is as follows:

#include "modifypropcmd.h"

modifypropcmd::modifypropcmd(mymainview *thisview, baseblockentity *item,QUndoCommand *parent)
    :QUndoCommand(parent),myGraphview(thisview),myitem(item)
{
}

void modifypropcmd::undo()
{

}

void modifypropcmd::redo()
{
}

This structure of a class is identical for over 100 different actions with undo commands.

This class when contained in a new class files does not work. It throws so many exceptions that i cannot understand. Here is a typical exception thrown.

C:\......\modifypropcmd.h:19: error: 'mymainview' does not name a type; did you mean 'mymainscene'?
.......\Commands/modifypropcmd.h:19:5: error: 'mymainview' does not name a type; did you mean 'mymainscene'?
     mymainview *myGraphview;
     ^~~~~~~~~~
     mymainscene

However, if i copy the entire class without any modification into another header and cpp file abc1.h and abc1.cpp which already has a similar class, the project compiles like a charm... without giving any errors.

Though I am able to continue working by creating these classes in existing files, I just dont know what could be the problem and i intend to solve it with help of experts here.

JonB

@TheCrowKaka
What are you doing?! :confused:

[BTW your problem won't be to do with QUndoCommand.]

class modifyblklaserpropcmd : public QUndoCommand
{
public:
    modifypropcmd(mymainview *thisview, baseblockentity *item,QUndoCommand *parent = 0);

This declares a new class named modifyblklaserpropcmd and then declares a constructor for class modifypropcmd and no constructor for modifyblklaserpropcmd....

And then in the .cpp you have the same: constructor for modifypropcmd, rest of methods for modifyblklaserpropcmd.

Can you start by sorting this out correctly, before we deal with #ifndef MODIFYPROPCMD_H which presumably should read #ifndef MODIFYBLKLASERPROPCMD_H, and why you have class modifyblklaserpropcmd in files named modifyprop...{cpp,h} and then there is a modifypropcmd.h file....

If this is all "deliberate" then I leave you to figure, because the architecture is too hard for me to get my head around.

If it's complaining error: 'mymainview' does not name a type then it has not met a class mymainview when it hits that line. If that is supposed to come from #include "mymainview.h" then my guess is that file has some complex #ifndef ... which in your scheme causes class mymainview not to have been encountered....

TheCrowKaka

@JonB SORRY for the trouble..

Happened due to the copy pasting affair.
I have corrected the post.

JonB

@TheCrowKaka said in Peculiar problem with QUndoCommand in a new class files.:

@JonB SORRY for the trouble..
Happened due to the copy pasting affair.

Grrrrrrr :@ Do you realize how many times I have answered people's posts, which are said to be a "copy/paste" of their code, and then turn out not to be, and I have spent all the time to answer...?

So we go back to my last paragraph:

If it's complaining error: 'mymainview' does not name a type then it has not met a class mymainview when it hits that line. If that is supposed to come from #include "mymainview.h" then my guess is that file has some complex #ifndef ... which in your scheme causes class mymainview not to have been encountered....

#include "mymainview.h"

class modifypropcmd: public QUndoCommand
{
private:
    mymainview *myGraphview;

C:\......\modifypropcmd.h:19: error: 'mymainview' does not name a type; did you mean 'mymainscene'?
.......\Commands/modifypropcmd.h:19:5: error: 'mymainview' does not name a type; did you mean 'mymainscene'?
     mymainview *myGraphview;
     ^~~~~~~~~~

So mymainview is not declared when it gets to modifypropcmd.h:19. So what exactly is in your "mymainview.h", if that is where it is supposed to come from ... ?

Christian Ehrlicher

@JonB said in Peculiar problem with QUndoCommand in a new class files.:

mymainview

simply forward declare the mymainview class.

JonB

@Christian-Ehrlicher
Since he has #include "mymainview.h" at the top of the file prior to mymainview *myGraphview; (as I pasted), don't you think that is supposed to bring in its declaration without any need/intention for forward declarations?? Which is why we need to see that file before deciding what the best "fix" is....

Christian Ehrlicher

@JonB said in Peculiar problem with QUndoCommand in a new class files.:

don't you think that is supposed to bring in its declaration without any need/intention for forward declarations??

No because he includes modifypropcmd.h inside mymainview.h so there is a circular dependency

JonB

@Christian-Ehrlicher said in Peculiar problem with QUndoCommand in a new class files.:

No because he includes modifypropcmd.h inside mymainview.h so there is a circular dependency

If that is the case your answer makes sense. But how in the world do you know that, since he has never shown mymainview.h?? Unless I am going mad and haven't spotted something.... [Or you are clairvoyant...]

Christian Ehrlicher

@JonB said in Peculiar problem with QUndoCommand in a new class files.:

Unless I am going mad and haven't spotted something....

I don't know it but it's a common error when you see such an error (you include a header, use the class but the compiler don't know about it).
There is no need to include a header file in another one when just the pointer to the class is used - use forward decls for such kind - it avoids circular dependency errors and speed up compilation.

JonB

@Christian-Ehrlicher said in Peculiar problem with QUndoCommand in a new class files.:

I don't know

Ah ha! Better :) So you never intended "No because he includes", rather "If he includes"...

@TheCrowKaka

If @Christian-Ehrlicher has been correctly clairvoyant about your mymainview.h having #include "modifypropcmd.h" in it then his is your answer.
OTOH, if you need a mere mortal like myself --- no super-powers --- to help still, unlike @Christian-Ehrlicher I need to actually see what is in your mymainview.h file....

:)

TheCrowKaka

@Christian-Ehrlicher, @JonB
Thanks for your answers.

I was about to type the elaborate answer, but while doing that i realised the error.

As @Christian-Ehrlicher indicated,
No because he includes modifypropcmd.h inside mymainview.h so there is a circular dependency

That was the exact problem.
I moved the modifypropcmd.h include from mymainview.h to mymainview.cpp and the solution compiled.

Thanks both for helping me out.

JonB

@TheCrowKaka said in Peculiar problem with QUndoCommand in a new class files.:

As @Christian-Ehrlicher indicated,
No because he includes modifypropcmd.h inside mymainview.h so there is a circular dependency
That was the exact problem.

I give up! If @Christian-Ehrlicher has enough telepathy to answer questions here without even seeing the code, what is the point in my even trying.... :( :) !!

Christian Ehrlicher

@JonB said in Peculiar problem with QUndoCommand in a new class files.:

what is the point in my even trying.... :( :) !!

:D

This is just more than 20 years of experience - don't know how often I hit this problem by myself until I switched to forward decl. nearly everything what's possible :)