Undefined reference to vtable, Qt in Linux

Question

I was trying to compile a Qt and OpenGL program under Code::Blocks in Ubuntu 10.04. I get the 'undefined reference to 'vtable for GLWidget'

#ifndef _GLWIDGET_H
#define _GLWIDGET_H

#include <QtOpenGL/QGLWidget>
#include "stdlib.h"

class GLWidget : public QGLWidget {

    Q_OBJECT // must include this if you use Qt signals/slots

public:
    GLWidget(QWidget *parent = 0);
    ~GLWidget();
protected:
    void initializeGL();
    void resizeGL(int w, int h);
    void paintGL();
    void keyPressEvent(QKeyEvent *event);
};

#endif  /* _GLWIDGET_H */

I borrowed the code from this guy to see if it works, because mine wasn't working because of the same reason. Code

And here is the GLWidget.cpp:

#include <QtGui/QMouseEvent>
#include "glwidget.h"

GLWidget::GLWidget(QWidget *parent) : QGLWidget(parent) {
    setMouseTracking(true);
}

GLWidget::~GLWidget()
{
}

void GLWidget::initializeGL() {
   ...
}

void GLWidget::resizeGL(int w, int h) {
   ...
}

void GLWidget::paintGL() {
    ...
}

void GLWidget::keyPressEvent(QKeyEvent* event) {
    ...
    }
}

I removed the code from the GL part to keep it shorter. Should you need it, I can always post it up.

#include <QtGui/QApplication>
#include <QtOpenGL/QGLWidget>
#include "glwidget.h"

int main(int argc, char *argv[]) {

    QApplication app(argc, argv);

    GLWidget window;
    window.resize(800,600);
    window.show();

    return app.exec();
}

Answer 1

In your project.pro file add

QT += opengl

So it knows that it has to link to GL libraries.

Answer 2

Clean your project and run qmake on it.

Answer 3

'undefined reference to 'vtable for GLWidget' most probably means that the definition of the first non inline virtual function of GLWidget isn't linked in the executable.

In the present case, my guess it is that it should be provided by the file generated by moc (but as I don't program for QT, I may be mistaken here).