Error: undefined reference to 'vtable for XXX'

[Kritika]

i have created a base class called Base which inherits from QDialog:
@
class Base : public QDialog
{
Q_OBJECT
public:
Base ();

--
};
@
And added this file to PATH: /usr/local/include/ and its source file to /usr/local/src/

Now I am using this as a base class in my application:
@
class Test:public Base
{
Q_OBJECT

--
};
@

The application is giving error:
undefined reference to 'vtable for A'.
Does anyone know why i am getting this error??

P.S. :--Here the Base class is not an abstract class.

[edit, code tags added, koahnig]

[koahnig]

Please check out the forum rules for "code wrappings.":http://qt-project.org/wiki/ForumHelp#e3f82045ad0f480d3fb9e0ac2d58fb01 This time I have added them for you.

This is a very general error message typically coming up when a class is not properly initialized yet. You need to check out the initialization of members in your class respectively if the sequence of their initialization is correct when doing a recursive initialization. For the last case you should have received a warning as long as the sequence is not correct within the class.

[andre]

One possible (and unfortunately common with Qt and qmake) cause is that qmake did not pick up the Q_OBJECT macro in your class declaration yet. If that is the case, then the Q_OBJECT macro is declaring some methods that are not implemented by moc yet.

Did you re-run qmake on your project before trying to rebuild?

[Kritika]

Yes...i tried that....but it is giving the same error on building d project.

[andre]

So, show the actual error please. My crystal ball is at the repair shop...

[butterface]

Do you have virtual methods?

[mranger90]

Are the above definitions in an include file or a .cpp file ?

[Kritika]

There is no virtual method, right now.
I am just testing how this concept works.
And these definitions are include file.

[Kritika]

base.h file
@#ifndef BASE_H
#define BASE_H

#include <QDialog>

class Base : public QDialog
{
Q_OBJECT
public:

protected:
explicit Base(QWidget *parent = 0, Qt::WindowFlags f = 0);

signals:

public slots:

};

#endif // BASE_H@

base.cpp file
@#include "base.h"

Base::Base(QWidget *parent, Qt::WindowFlags f):
QDialog(parent, f)
{
}@

Added base.h in PATH: /usr/local/include/ and base.cpp in PATH:/usr/local/src/.., since i dont want to add this base class in my application explicitely.

TestBase project:
This is the class inherits Base class:
test.h file
@#ifndef TEST_H
#define TEST_H

#include "base.h"

class Test : public Base
{
Q_OBJECT

public:
explicit Test(QWidget *parent = 0);
~Test();

private:
};
#endif // TEST_H
@

test.cpp file":
@#include "test.h"

Test::Test(QWidget *parent) :
Base(parent, Qt::FramelessWindowHint ),
{
}

Test::~Test()
{
}
@

main.cpp:
@#include <QtGui/QApplication>
#include "dialog.h"

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Dialog w;
w.show();

return a.exec();

}
@

Errors after make command:
test.o: In function Test::~Test()': test.cpp:(.text+0x1f): undefined reference to vtable for Base'
test.cpp:(.text+0x27): undefined reference to vtable for Base' test.o: In function Test::Test(QWidget*)':
test.cpp:(.text+0x96): undefined reference to Base::Base(QWidget*, QFlags<Qt::WindowType>)' test.cpp:(.text+0xee): undefined reference to vtable for Base'
test.cpp:(.text+0xf6): undefined reference to vtable for Base' moc_test.o: In function Test::qt_metacall(QMetaObject::Call, int, void**)':
moc_test.cpp:(.text+0x31): undefined reference to Base::qt_metacall(QMetaObject::Call, int, void**)' moc_test.o: In function Test::qt_metacast(char const*)':
moc_test.cpp:(.text+0x77): undefined reference to Base::qt_metacast(char const*)' moc_test.o:(.rodata+0x20): undefined reference to Base::staticMetaObject'
moc_test.o:(.rodata._ZTI4Test[typeinfo for Test]+0x10): undefined reference to `typeinfo for Base'
collect2: ld returned 1 exit status
make: *** [testMMIBase] Error 1

[andre]

[quote author="Kritika" date="1391494986"]Added base.h in PATH: /usr/local/include/ and base.cpp in PATH:/usr/local/src/.., since i dont want to add this base class in my application explicitely.
[/quote]
That is interesting. What do you mean by that? Do you mean that you're not actually compiling in base.h and base.cpp into your application? If so: that won't work. If you don't want Base in your main application, you'll need to put it in a library that you link against. Otherwise, how is your application to know at run time what base actually is?

[JKSH]

If you don't include base.h and base.cpp in your project directory, then they will not be compiled.

You have two options:

Put base.h and base.cpp in your project directory.

Compile base.h and base.cpp into an an external library. Then, link that library to your project.

[Kritika]

@JKSH- Thanks....
Like u said, i compiled this base class, this created four versioned libraries:
libbase.so
libbase.so.1
libbase.so.1.0
libbase.so.1.0.0
and then, i linked the TestBase project against it. The application did build successfully, but giving another error on run:

"error while loading shared libraries: libbase.so.1: cannot open shared object file: no such file or directory"

Can anybody explain why i am getting this error..

[andre]

The shared library can't be found. So, you'll need to deploy it to a location where it can be found.

[Kritika]

The problem is fixed..
Now, i am adding library in the application by the option Add Library on right click. This is linking library as well as including header file. And this is working well...Although i still couldnt figure out why previous thing was not working.

[JKSH]

[quote author="Kritika" date="1391529236"]The problem is fixed..[/quote]Great! :)

[quote]Although i still couldnt figure out why previous thing was not working.[/quote]Because you didn't tell your program where to find the library previously.