Strange linker error - can anyone help? (Qt 4.1.2)

[Dr. Norbert Prang]

Hello,

is there anybody, who can explain to me the cause for the following strange linker error in my Xcode based Qt project?

/usr/bin/ld: Undefined symbols:
vtable for GoButton
/Users/Norbert/MyCode/SlotTest01/build/SlotTest01.build/Debug/SlotTest01.build/Objects-normal/ppc/main.o reference to undefined vtable for GoButton
collect2: ld returned 1 exit status
/usr/bin/ld: Undefined symbols:
vtable for GoButton
/Users/Norbert/MyCode/SlotTest01/build/SlotTest01.build/Debug/SlotTest01.build/Objects-normal/ppc/main.o reference to undefined vtable for GoButton
collect2: ld returned 1 exit status


For better understanding:

I intended to make just a simple program for testing selfmade slots. The code of the main.cpp ist the following:

#include <qapplication.h>
#include <qpushbutton.h>
#include <qobject.h>
#include <qstring.h>
#include <qwidget.h>

#include <unistd.h>

class GoButton : public QPushButton
{
Q_OBJECT
public:
GoButton(const QString& text, QWidget* parent)
: QPushButton(text, parent)
{
connect(this, SIGNAL(clicked()), this, SLOT(go()));
}
public slots:
void go()
{
static int count = 0;
count++;

if(count > 5)
{
qApp->quit(); //Finish after 5th click
}

}

};

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

GoButton* b = new GoButton("Press Me, Please!", 0);

b->show();

QObject::connect(qApp, SIGNAL(lastWindowClosed()), qApp, SLOT(quit()));

return a.exec();
}



I made a Xcode project by processing the main.cpp as the only file in my project directory as follows:

I typed: qmake –project

The resulting Qt .pro file looks as follows:

################################################## ####################
# Automatically generated by qmake (2.00a) Fri Jun 16 13:07:34 2006
################################################## ####################

TEMPLATE = app
TARGET +=
DEPENDPATH += .
INCLUDEPATH += .

# Input
SOURCES += main.cpp

Then I typed: qmake

Then I opened the Xcode project and started a build process. All compiler action seemed to be o. k..The linker error above occured.


I cannot explain to me, what could be wrong here.

Can anyone? I hope ...

Have a nice weekend, you all!

Norbert

[jacek]

You must run moc utility on every class that contains Q_OBJECT macro to generate missing code. Usually qmake does this for you, but unfortunately it only checks header files for Q_OBJECT, so moc won't be run if you have a class definition inside a .cpp file.

The easiest solution is to add #include "main.moc" at the end of main.cpp file (don't forget to rerun qmake). This tells qmake that it has to run moc on given file.

[Dr. Norbert Prang]

Hi,

thanks for quick and useful reply! That works really phantastic. Thanks again.

Have a nice weekend.
Norbert :)