[Qt-interest] Frequent error - help pls

[Spulber Iosif]

Ok, so I tried some stuff and I got some things, but anyways here's the code:

~~~~~~~~~~~~~
#ifndef QUESTION_H
#define QUESTION_H


class QuestionData
{
public:
    QString QuestionText;
};
class Question
{
public:
    enum Type {TrueFalse, SingleChoice};
    Type QuestionType;
    QuestionData *Data;
    void LoadData (Question *Data);
private:
    virtual void Save ();
};

class SingleChoiceData: public QuestionData
{
public:
    int NumberOfAnswers;
    int Correct;
    QString Answers[10];
};

class TrueFalseData: public QuestionData
{
public:
    bool Correct;
    QString Answer1, Answer2;
};

#endif // QUESTION_H
~~~~~~~~~~~~~~

The problem arises when I try to declare any Question object; it says :
D:/Qt/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/locale_facets.tcc:2498: undefined reference to `vtable for Question'

The compile output:
Running build steps for project QuizMaker...
Configuration unchanged, skipping QMake step.
Starting: D:/Qt/mingw/bin/mingw32-make.exe -w 
mingw32-make: Entering directory `C:/Documents and Settings/TheBlackElf/My Documents/QuizMaker'
D:/Qt/mingw/bin/mingw32-make -f Makefile.Debug
mingw32-make[1]: Entering directory `C:/Documents and Settings/TheBlackElf/My Documents/QuizMaker'
g++ -c -g -frtti -fexceptions -mthreads -Wall -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"d:\Qt\qt\include\QtCore" -I"d:\Qt\qt\include\QtGui" -I"d:\Qt\qt\include" -I"d:\Qt\qt\include\ActiveQt" -I"debug" -I"d:\Qt\qt\mkspecs\win32-g++" -o debug\main.o main.cpp
g++ -c -g -frtti -fexceptions -mthreads -Wall -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"d:\Qt\qt\include\QtCore" -I"d:\Qt\qt\include\QtGui" -I"d:\Qt\qt\include" -I"d:\Qt\qt\include\ActiveQt" -I"debug" -I"d:\Qt\qt\mkspecs\win32-g++" -o debug\mainwindow.o mainwindow.cpp
g++ -c -g -frtti -fexceptions -mthreads -Wall -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"d:\Qt\qt\include\QtCore" -I"d:\Qt\qt\include\QtGui" -I"d:\Qt\qt\include" -I"d:\Qt\qt\include\ActiveQt" -I"debug" -I"d:\Qt\qt\mkspecs\win32-g++" -o debug\truefalse.o truefalse.cpp
g++ -c -g -frtti -fexceptions -mthreads -Wall -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"d:\Qt\qt\include\QtCore" -I"d:\Qt\qt\include\QtGui" -I"d:\Qt\qt\include" -I"d:\Qt\qt\include\ActiveQt" -I"debug" -I"d:\Qt\qt\mkspecs\win32-g++" -o debug\singlechoice.o singlechoice.cpp
D:/Qt/qt/bin\moc.exe -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"d:\Qt\qt\include\QtCore" -I"d:\Qt\qt\include\QtGui" -I"d:\Qt\qt\include" -I"d:\Qt\qt\include\ActiveQt" -I"debug" -I"d:\Qt\qt\mkspecs\win32-g++" -D__GNUC__ -DWIN32 mainwindow.h -o debug\moc_mainwindow.cpp
g++ -c -g -frtti -fexceptions -mthreads -Wall -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_GUI_LIB -DQT_CORE_LIB -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"d:\Qt\qt\include\QtCore" -I"d:\Qt\qt\include\QtGui" -I"d:\Qt\qt\include" -I"d:\Qt\qt\include\ActiveQt" -I"debug" -I"d:\Qt\qt\mkspecs\win32-g++" -o debug\moc_mainwindow.o debug\moc_mainwindow.cpp
g++ -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -mthreads -Wl -Wl,-subsystem,windows -o debug\QuizMaker.exe debug/main.o debug/mainwindow.o debug/truefalse.o debug/singlechoice.o debug/moc_mainwindow.o -L"d:\Qt\qt\lib" -lmingw32 -lqtmaind -lQtGuid4 -lQtCored4
mingw32-make[1]: Leaving directory `C:/Documents and Settings/TheBlackElf/My Documents/QuizMaker'
mingw32-make: Leaving directory `C:/Documents and Settings/TheBlackElf/My Documents/QuizMaker'
~~~~~~~ here it gets red:
debug/mainwindow.o: In function `ZSt17__verify_groupingPKcjRKSs':
D:/Qt/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../../include/c++/3.4.5/bits/locale_facets.tcc:2498: undefined reference to `vtable for Question'
collect2: ld returned 1 exit status
mingw32-make[1]: *** [debug\QuizMaker.exe] Error 1
mingw32-make: *** [debug] Error 2
Exited with code 2.
Error while building project QuizMaker
When executing build step 'Make'
~~~~~~~~

To explain how it occoured (and I think last time it did the same): I wanted a slot in Question so I inserted Q_OBJECT in the beginning. It didn't recognize Q_OBJECT (btw, what header do I need just for that?). I thought <QApplication> or <QPushButton> should include the macro somehow, but it said that "Q_OBJECT is not inherited through <...>". I then deleted the header inclusion and Q_OBJECT and it produced that error since.
Now I discovered that if I make Save () non-virtual everything is OK. But I really need the virtual function. Also, if I try to declare virtual functions in other classes in the same header it doesn't work as well.

Best regards,
Iosif Spulber



      
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