Undefined reference to vtable. Trying to compile a Qt project

C++ Problem Overview

I'm using Code::Blocks 8.02 and the mingw 5.1.6 compiler. I'm getting this error when I compile my Qt project:

> C:\Documents and Settings\The > Fuzz\Desktop\GUI\App_interface.cpp|33|undefined > reference to `vtable for AddressBook'

File AddressBook.h:

 #ifndef ADDRESSBOOK_H
 #define ADDRESSBOOK_H

 #include <QWidget>

 class QLabel;
 class QLineEdit;
 class QTextEdit;

 class AddressBook : public QWidget
 {
     Q_OBJECT

 public:
     AddressBook(QWidget *parent = 0);

 private:
     QLineEdit *nameLine;
     QTextEdit *addressText;
 };

 #endif

File AddressBook.cpp:

#include <QtGui>
#include "addressbook.h"

AddressBook::AddressBook(QWidget *parent)
     : QWidget(parent)
{
    QLabel *nameLabel = new QLabel(tr("Name:"));
    nameLine = new QLineEdit;

    QLabel *addressLabel = new QLabel(tr("Address:"));
    addressText = new QTextEdit;

    QGridLayout *mainLayout = new QGridLayout;
    mainLayout->addWidget(nameLabel, 0, 0);
    mainLayout->addWidget(nameLine, 0, 1);
    mainLayout->addWidget(addressLabel, 1, 0, Qt::AlignTop);
    mainLayout->addWidget(addressText, 1, 1);

    setLayout(mainLayout);
    setWindowTitle(tr("Simple Address Book"));
}

C++ Solutions

Solution 1 - C++

When using Qt Creator:

Build → Run qmake
Build → Rebuild All

Solution 2 - C++

Warning: Do not do this if you already have a .pro file - you'll lose it!

In order to automatically ensure that all moc cpp files are generated, you can get qmake to automatically generate a .pro file for you instead of writing one yourself.

Run

qmake -project

in the project directory, and qmake will scan your directory for all C++ headers and source files to generate moc cpp files for.

Solution 3 - C++

The problem is almost certainly that you are not compiling or not linking in the generated moc_AddressBook.cpp file. (It should have been generated for you -- you are running Qt's moc on your code before compiling, right?)

To answer a little more thoroughly, the Q_OBJECT macro signals Qt's moc tool to create an extra implementation file that contains the code necessary to support QObject's meta-information system. If you had any signals or slots, it would do a few things for those as well.

An alternative solution might be to remove the Q_OBJECT macro. You probably don't want to do this, but it would help the immediate problem, and it isn't strictly necessary with the code that you've presented.

Also, I would note that your line:

#include "addressbook.h"

Should probably be:

#include "AddressBook.h"

based on how you presented the filenames in the question.

Solution 4 - C++

Assuming you are using qmake to generate your Makefile, be sure that AddressBook.h is specified in your .pro file's HEADERS's variable, e.g.

HEADERS = AddressBook.h

Solution 5 - C++

For CMake projects, set CMAKE_AUTOMOC to ON, this fixed my problem.

#Find includes in corresponding build directories
set(CMAKE_INCLUDE_CURRENT_DIR ON)

# Instruct CMake to run moc automatically when needed.
set(CMAKE_AUTOMOC ON)

Solution 6 - C++

I got this while using pure virtual functions. For example,

virtual void process();

gave this error, while

virtual void process() = 0;

made it go away.

For anyone who's Googling this problem, check that all virtual functions are defined. (via " = 0" or a full definition in the source file) I'm using Netbeans with the MinGW compiler.

Solution 7 - C++

I was running into the same problem using CLion, and solved it by adding these lines to CMakeLists.txt

set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTORCC ON)

See https://www.jetbrains.com/help/clion/qt-tutorial.html#qt-setup-in-clion

Solution 8 - C++

I had the same problem but as soon as I defined my constructor in the header file instead of the .cpp the error disappeared. Also the corresponding moc file was missing in the file system and in the Makefile section"compiler_moc_header_make_all" . I ran a qmake then finally everything built with succes. I went to check the Makefile and it was there now.

Solution 9 - C++

deleted the build folder, restarted Qt Creator and it worked

Solution 10 - C++

I come to the same problem, rebuild the project never update the Makefile, I remove the Makefile and rebuild , the the problem is gone. ps: run 'make' from command line may give you detail information than the IDE, and helpful to get the real problem.

Solution 11 - C++

One cause is when you declare a virtual functions in a class and you don't define their body.

Solution 12 - C++

In my case Rebuild All was not enough, I had to delete build directory and make Rebuild All - then it worked!

Solution 13 - C++

Simply Run qmake for your project. This can easily be done by right-clicking on the name of your project and clicking on Run qmake.

Solution 14 - C++

Just clear the project and then rebuild it!

Solution 15 - C++

Go to .pro file and make sure .h file has 'include' before it. HEADERS += include/file.h
include/file2.h

Solution 16 - C++

I had the same problem trying to use a protected virtual function. Two things worked.

Changing void process(); to void process() = 0;
Making process() public instead of private

Solution 17 - C++

You will get the same error message if you accidentally add a destructor prototype. Add an empty destructor definition or remove the prototype.

Solution 18 - C++

Header files for moc compilation should contained in the HEADERS += ... variable:

I have moved the header files in the Myproject.pro to the SOURCES += ... section, because I want to have mySource.h and mySource.cpp in the same tree element. But that is faulty for QT Creator. In result the error "Undefined reference to vtable" has occured. It seems to be: QT detects header for moc compilation only in the HEADERS +=... section (or variable). See also the correct explaination in the other stackoverflow answer Second anwer "I've seen a lot of ways to solve the problem, but no explanation for why it happens, so here goes.". In my mind this is an exactly explaination of the problem, which has help me to found and solve my problem.

Solution 19 - C++

CMake

when using CMake, interestingly enough if my .cpp and .h files are not in the same folder the moc, bu default, fails to generate the meta file :)

Solution 20 - C++

the most errors from using Q_OBJECT but not generate moc file
the moc file define
classname::metaObject
staticMetaObject
qt_metacall

Here is a example:
when source or header using Q_OBJECT

/opt/qt/bin/moc ./window.h -o ./moc_window.cpp

Makefile add moc_window.o in OBJS
Ex: OBJS=main.o window.o moc_window.o

try this source
https://www.mediafire.com/file/anjeah1jmm07mfe/qt_group_box.tar.gz

refer to http://fatalfeel.blogspot.com/2013/11/qt5-c-building.html

Solution 21 - C++

I am using Qt creator to compile and run my programs, I don't use Qt command prompt often. One thing I did to get rid of the annoying error "vtable something something" is by adding the following lines to .pro file.

> TEMPLATE = app

> QT += core

Content Type	Original Author	Original Content on Stackoverflow
Question	TheFuzz	View Question on Stackoverflow
Solution 1 - C++	Anurag Verma	View Answer on Stackoverflow
Solution 2 - C++	blwy10	View Answer on Stackoverflow
Solution 3 - C++	Caleb Huitt - cjhuitt	View Answer on Stackoverflow
Solution 4 - C++	Jeremy Friesner	View Answer on Stackoverflow
Solution 5 - C++	Dumisani Kunene	View Answer on Stackoverflow
Solution 6 - C++	user688627	View Answer on Stackoverflow
Solution 7 - C++	Felipe C.	View Answer on Stackoverflow
Solution 8 - C++	yan bellavance	View Answer on Stackoverflow
Solution 9 - C++	yolo	View Answer on Stackoverflow
Solution 10 - C++	user281754	View Answer on Stackoverflow
Solution 11 - C++	agus	View Answer on Stackoverflow
Solution 12 - C++	Aleksei Petrenko	View Answer on Stackoverflow
Solution 13 - C++	Sunit Gautam	View Answer on Stackoverflow
Solution 14 - C++	Hamed	View Answer on Stackoverflow
Solution 15 - C++	Phil	View Answer on Stackoverflow
Solution 16 - C++	khafen	View Answer on Stackoverflow
Solution 17 - C++	Emil Fors	View Answer on Stackoverflow
Solution 18 - C++	Hartmut Schorrig	View Answer on Stackoverflow
Solution 19 - C++	Goran Shekerov	View Answer on Stackoverflow
Solution 20 - C++	YU Chen Shih	View Answer on Stackoverflow
Solution 21 - C++	Mmakgabo Makgoba	View Answer on Stackoverflow