compile a Qt single file from command line: undefined reference to vtable

Question

I'd like to compile a single file QT application from command line, for test in a quick way some features. See the code of the file below.

I'm compiling with:

qmake -project && qmake && make

And I' getting this error:

Togglebutton.o:Togglebutton.cpp:function ButtonDialog::ButtonDialog(QWidget*): error: undefined reference to 'vtable for ButtonDialog'
Togglebutton.o:Togglebutton.cpp:function ButtonDialog::ButtonDialog(QWidget*): error: undefined reference to 'vtable for ButtonDialog'
Togglebutton.o:Togglebutton.cpp:function ButtonDialog::~ButtonDialog(): error: undefined reference to 'vtable for ButtonDialog'
Togglebutton.o:Togglebutton.cpp:function ButtonDialog::~ButtonDialog(): error: undefined reference to 'vtable for ButtonDialog'

I'm not a c++ guru, I've tried to google about undefined reference to vtable but I don't understad why I'm getting this error also with one file..

Someone can help me in understaning the undefined vtable error?

/*
 * Copyright (c) 2006-2007, Johan Thelin
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification, 
 * are permitted provided that the following conditions are met:
 * 
 *     * Redistributions of source code must retain the above copyright notice, 
 *       this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright notice,  
 *       this list of conditions and the following disclaimer in the documentation 
 *       and/or other materials provided with the distribution.
 *     * Neither the name of APress nor the names of its contributors 
 *       may be used to endorse or promote products derived from this software 
 *       without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include <QPushButton>
#include <QHBoxLayout>
#include <QMessageBox>

#include <QApplication>
#include <QDialog>
class QPushButton;

class ButtonDialog : public QDialog
{
  Q_OBJECT

public:
  ButtonDialog( QWidget *parent=0 );

private slots:
  void buttonClicked();
  void buttonToggled();

private:
  QPushButton *clickButton;
  QPushButton *toggleButton;
};

ButtonDialog::ButtonDialog( QWidget *parent ) : QDialog( parent )
{
  clickButton = new QPushButton( "Click me!", this );
  toggleButton = new QPushButton( "Toggle me!", this );
  toggleButton->setCheckable( true );

  QHBoxLayout *layout = new QHBoxLayout( this );
  layout->addWidget( clickButton );
  layout->addWidget( toggleButton );

  connect( clickButton, SIGNAL(clicked()), this, SLOT(buttonClicked()) );
  connect( toggleButton, SIGNAL(clicked()), this, SLOT(buttonToggled()) );
}

void ButtonDialog::buttonClicked()
{
  QMessageBox::information( this, "Clicked!", "The button was clicked!" );
}

void ButtonDialog::buttonToggled()
{
  QMessageBox::information( this, "Toggled!", QString("The button is %1!").arg(toggleButton->isChecked()?"pressed":"released") );
}


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

  ButtonDialog dlg;
  dlg.show();

  return app.exec();
}

Answer 1

I had the same mistake, when I declared a Q_OBJECT class in cpp file. Create a header and move class declaration there.