Undifined Refrence: vtable

[mweber1488]

I just started learning Qt and I have been working through the example on this page: http://doc.qt.nokia.com/4.7/gettingstartedqt.html
The problem is that when I get to sub classing QWidget I start getting the following linker errors:

notepad.cpp|3|undefined reference to `vtable for Notepad'|
obj\Debug\notepad.o:C:\programming\c\test\notepad. h|10|undefined reference to `Notepad::staticMetaObject'|

The code is exactly the same as the examples, I am using Qt 4.7.1 and codeblocks as the ide.

[tbscope]

Clean you project (that is, remove any generated files), run qmake again, rebuild

[nroberts]

I just started learning Qt and I have been working through the example on this page: http://doc.qt.nokia.com/4.7/gettingstartedqt.html
The problem is that when I get to sub classing QWidget I start getting the following linker errors:

notepad.cpp|3|undefined reference to `vtable for Notepad'|
obj\Debug\notepad.o:C:\programming\c\test\notepad. h|10|undefined reference to `Notepad::staticMetaObject'|

The code is exactly the same as the examples, I am using Qt 4.7.1 and codeblocks as the ide.

The moc output for notepad isn't getting linked in.

[squidge]

The moc output for notepad isn't getting linked in.

and the solution to fix that is in post #2

[Zlatomir]

When you sub-class don't forget the Q_OBJECT macro:

class Notepad : public QWidget        {
           Q_OBJECT   //this one is important if you use signals/slots or other qmetaobject goodies
//.... rest of the class definition

class Notepad : public QWidget        {
           Q_OBJECT   //this one is important if you use signals/slots or other qmetaobject goodies
//.... rest of the class definition

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Also for each class use a header .h file for declaration and a .cpp file for definitions.

If you write classes with Q_OBJECT in the main.cpp file (a and have only that one .cpp file) you should use:

#include "main.moc"

#include "main.moc"

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at the end of the .cpp file
Replace main.cpp with YourFileName.cpp

[mweber1488]

and the solution to fix that is in post #2

Actually its not as

codeblocks as the ide

and doesn't use qmake.
So I figure out the moc thing just before I looked here as I tried building under QtCreator but now I am getting the following error (in both QtCreator and codeblocks):

debug/moc_notepad.o:C:\programming\c\test\test-build-desktop/debug/moc_notepad.cpp:74: undefined reference to `Notepad::open()'
 
debug/moc_notepad.o:C:\programming\c\test\test-build-desktop/debug/moc_notepad.cpp:75: undefined reference to `Notepad::save()'
 
debug/moc_notepad.o:C:\programming\c\test\test-build-desktop/debug/moc_notepad.cpp:76: undefined reference to `Notepad::quit()'

debug/moc_notepad.o:C:\programming\c\test\test-build-desktop/debug/moc_notepad.cpp:74: undefined reference to `Notepad::open()'

debug/moc_notepad.o:C:\programming\c\test\test-build-desktop/debug/moc_notepad.cpp:75: undefined reference to `Notepad::save()'

debug/moc_notepad.o:C:\programming\c\test\test-build-desktop/debug/moc_notepad.cpp:76: undefined reference to `Notepad::quit()'

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For completeness here is the entire code:
notepad.h

#ifndef _NOTEPAD_H_
#define _NOTEPAD_H_
 
#include <QtGui>
 
class Notepad: public QMainWindow
{
    Q_OBJECT
 
    public:
        Notepad();
 
    private slots:
        void open();
        void save();
        void quit();
 
    private:
        QTextEdit   *textEdit;      // The text editor
 
        QAction     *openAction;    // For the widgets that perform open
        QAction     *saveAction;    // Save shit
        QAction     *quitAction;    // Quit shit
 
        QMenu *fileMenu;            // Holds the menu options
};
 
#endif

#ifndef _NOTEPAD_H_
#define _NOTEPAD_H_

#include <QtGui>

class Notepad: public QMainWindow
{
    Q_OBJECT

    public:
        Notepad();

    private slots:
        void open();
        void save();
        void quit();

    private:
        QTextEdit   *textEdit;      // The text editor

        QAction     *openAction;    // For the widgets that perform open
        QAction     *saveAction;    // Save shit
        QAction     *quitAction;    // Quit shit

        QMenu *fileMenu;            // Holds the menu options
};

#endif

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notepad.cpp

#include "notepad.h"
 
Notepad::Notepad()
{
    // Do the actions first
    openAction = new QAction(tr("&Open"), this);
    saveAction = new QAction(tr("&Sace"), this);
    quitAction = new QAction(tr("E&xit"), this);
 
    // Now connect the signals to the actions
    connect(openAction, SIGNAL(triggered()), this, SLOT(open()));
    connect(saveAction, SIGNAL(triggered()), this, SLOT(save()));
    connect(quitAction, SIGNAL(triggered()), qApp, SLOT(quit()));
 
    // Now set the menu bar
    fileMenu = menuBar()->addMenu(tr("&File"));
    fileMenu->addAction(openAction);
    fileMenu->addAction(saveAction);
    fileMenu->addSeparator();
    fileMenu->addAction(quitAction);
 
    textEdit = new QTextEdit;
    setCentralWidget(textEdit);
 
    setWindowTitle(tr("Notepad"));
}

#include "notepad.h"

Notepad::Notepad()
{
    // Do the actions first
    openAction = new QAction(tr("&Open"), this);
    saveAction = new QAction(tr("&Sace"), this);
    quitAction = new QAction(tr("E&xit"), this);

    // Now connect the signals to the actions
    connect(openAction, SIGNAL(triggered()), this, SLOT(open()));
    connect(saveAction, SIGNAL(triggered()), this, SLOT(save()));
    connect(quitAction, SIGNAL(triggered()), qApp, SLOT(quit()));

    // Now set the menu bar
    fileMenu = menuBar()->addMenu(tr("&File"));
    fileMenu->addAction(openAction);
    fileMenu->addAction(saveAction);
    fileMenu->addSeparator();
    fileMenu->addAction(quitAction);

    textEdit = new QTextEdit;
    setCentralWidget(textEdit);

    setWindowTitle(tr("Notepad"));
}

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main.cpp

#include "notepad.h"
 
int main(int argc, char ** argv)
{
    QApplication app(argc, argv);
 
    Notepad notepad;
    notepad.show();
 
    return app.exec();
}

#include "notepad.h"

int main(int argc, char ** argv)
{
    QApplication app(argc, argv);

    Notepad notepad;
    notepad.show();

    return app.exec();
}

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[norobro]

The error messages you are getting now tell you what is wrong:

undefined reference to `Notepad:: open()'

You've declared your slots but you haven't defined them.

[mweber1488]

Ahh, the example I have been following failed to mention that and I have been using D for so long that I am not used to classes being in stops. Thanks for all the help folks.

[tbscope]

As always:
1. Learn how your tools work
2. Provide all your information if you want help. My crystal ball often doesn't see if you use qmake or not.

[squidge]

It is always recommended that if your just getting started with Qt, you should make life at least a little easier for yourself by using the Qt SDK (ie, Qt Creator) and THEN moving to your preferred IDE when you understand how everything works rather than trying to jump in with a new framework from the start.

[nroberts]

I am not used to classes being in stops.

What be this?