Qt Undefined Reference to vtable

**Archimedes** · 24th February 2010, 20:25

What happens if you include QObject and make Jaus_neighbor a subclass of QObject?

**ctote** · 24th February 2010, 20:42

Originally Posted by Archimedes

What happens if you include QObject and make Jaus_neighbor a subclass of QObject?

Now I get an error saying multiple constructors defined:
multiple definition of `Jaus_neighbor::Jaus_neighbor()

Qt Code:

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Jaus_neighbor::Jaus_neighbor()
{
    udpSocket = new QUdpSocket(this);
    for (int i = 0; i < 4; i++)
    {
        head.dest_id[i] = 0;
        head.source_id[i] = 0;
    }
    head.sequence_num = 0;
    head.data_control = 0;
    head.message_properties = 0;
    head.command_code = NULL;
}

Jaus_neighbor::Jaus_neighbor()
{
    udpSocket = new QUdpSocket(this);
    for (int i = 0; i < 4; i++)
    {
        head.dest_id[i] = 0;
        head.source_id[i] = 0;
    }
    head.sequence_num = 0;
    head.data_control = 0;
    head.message_properties = 0;
    head.command_code = NULL;
}

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**ctote** · 24th February 2010, 20:45

Nevermind - I commented out the default constructor and I get the same error

**bmhautz** · 24th February 2010, 21:06

I was getting the same error with a custom table model (but only one out of 5, go figure).

Try the following:

1) See if it compiles correctly if you take out the Q_OBJECT define (and you may want to comment out the signals and slots as well).
2) If it compiles, then the moc compiler could be causing problems, so see if the following fixes it:
a) Specify CONFIG += release in the pro file.
b) Put the destructor definition in the header file (ie. ~MyClass(){})

This worked for me compiling with Qt 4.5.3. If you want to build debug as well just change CONFIG += release build_all -> this builds the release version first, then the debug version, which seems to help.

EDIT: I forgot to add that Jaus_neighbor must inherit from QObject.

**ctote** · 24th February 2010, 21:14

commented it out and i still get the same error

**Archimedes** · 24th February 2010, 21:17

Post the last version of the code of jaus.h and jaus.cpp

**bmhautz** · 24th February 2010, 21:18

It may be useful to post updated code with a note of what changed and the specific errors you are getting.

**ctote** · 24th February 2010, 21:42

Here's my updated code:

Qt Code:

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#ifndef JAUS_H
#define JAUS_H
 
#include <QtNetwork>
#include <QUdpSocket>
#include <QObject>
 
struct Jaus_header
{
    unsigned short message_properties;
    unsigned short command_code;
    QByteArray dest_id[4];
    QByteArray source_id[4];
    unsigned short data_control;
    unsigned short sequence_num;
};
 
class Jaus_neighbor : public QObject
{
    Q_OBJECT
 
public:    
    void handshake();
    void capabilities_discover();
    void sys_management();
    void close_conn();
 
private:
    Jaus_header head;
 
    QUdpSocket *udpSocket;
 
private slots:
    Jaus_neighbor();
 
    void prepare_header();
    void read_jheader();
    void send_jheader();
 
    void do_command();
    void startBroadcasting();
    void stopBroadcasting();
    void sendDatagram();
    //void verifyDatagram();
};
 
#endif // JAUS_H

#ifndef JAUS_H
#define JAUS_H

#include <QtNetwork>
#include <QUdpSocket>
#include <QObject>

struct Jaus_header
{
    unsigned short message_properties;
    unsigned short command_code;
    QByteArray dest_id[4];
    QByteArray source_id[4];
    unsigned short data_control;
    unsigned short sequence_num;
};

class Jaus_neighbor : public QObject
{
    Q_OBJECT

public:    
    void handshake();
    void capabilities_discover();
    void sys_management();
    void close_conn();

private:
    Jaus_header head;

    QUdpSocket *udpSocket;

private slots:
    Jaus_neighbor();

    void prepare_header();
    void read_jheader();
    void send_jheader();

    void do_command();
    void startBroadcasting();
    void stopBroadcasting();
    void sendDatagram();
    //void verifyDatagram();
};

#endif // JAUS_H

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Qt Code:

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#include "jaus.h"
 
Jaus_neighbor::Jaus_neighbor()
{
    udpSocket = new QUdpSocket(this);
    for (int i = 0; i < 4; i++)
    {
        head.dest_id[i] = 0;
        head.source_id[i] = 0;
    }
    head.sequence_num = 0;
    head.data_control = 0;
    head.message_properties = 0;
    head.command_code = 0;
}
 
void Jaus_neighbor::startBroadcasting()
{
 
}
 
void Jaus_neighbor::stopBroadcasting()
{
 
}
 
void Jaus_neighbor::sendDatagram()
{
    //udpSocket->writeDatagram(message, QHostAddress::LocalHost, 9000);
}
 
 
void Jaus_neighbor::handshake()
{
    Jaus_neighbor::startBroadcasting();
}

#include "jaus.h"

Jaus_neighbor::Jaus_neighbor()
{
    udpSocket = new QUdpSocket(this);
    for (int i = 0; i < 4; i++)
    {
        head.dest_id[i] = 0;
        head.source_id[i] = 0;
    }
    head.sequence_num = 0;
    head.data_control = 0;
    head.message_properties = 0;
    head.command_code = 0;
}

void Jaus_neighbor::startBroadcasting()
{

}

void Jaus_neighbor::stopBroadcasting()
{

}

void Jaus_neighbor::sendDatagram()
{
    //udpSocket->writeDatagram(message, QHostAddress::LocalHost, 9000);
}


void Jaus_neighbor::handshake()
{
    Jaus_neighbor::startBroadcasting();
}

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Qt Code:

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#include <QtCore/QCoreApplication>
#include <iostream>
#include "jaus.h"
using namespace std;
 
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
 
    cout << "Initializing Jaus Connections..." << flush;
    //Jaus_neighbor cop;
 
    return a.exec();
}

#include <QtCore/QCoreApplication>
#include <iostream>
#include "jaus.h"
using namespace std;

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

    cout << "Initializing Jaus Connections..." << flush;
    //Jaus_neighbor cop;

    return a.exec();
}

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I'm still getting the warnings -- but more importantly I think, is I'm getting the following error also: error: collect2: ld returned 1 exit status
If I comment out my default constructor, the app compiles fine.

**Archimedes** · 24th February 2010, 21:57

You have your constructor in private slots, that means when you declare an Jaus_neighbor object you can't access the constructor cause it's private. So move it to public.
Also you're getting undefined references for the functions prepare_header(), read_jheader(), send_jheader() and do_command() because there aren't implementation for those functions in the jaus.cpp.

**ctote** · 24th February 2010, 22:02

Thanks for the info -- I moved the constructor to public: but I still get the same error

**Archimedes** · 24th February 2010, 22:09

I copy pasted the code you gave. I moved the constructor to public, provided the implementation for the functions I told in the previous post ( put in the .cpp file eg.
void Jaus_neighbor:

repare_header() {} and so on) and compiled with success!

**ctote** · 24th February 2010, 22:22

well that's just not fair then!

here's my new .cpp file (and i moved the constructor):

Qt Code:

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#include "jaus.h"
 
Jaus_neighbor::Jaus_neighbor()
{
    udpSocket = new QUdpSocket(this);
    for (int i = 0; i < 4; i++)
    {
        header.dest_id[i] = 0;
        header.source_id[i] = 0;
    }
    header.sequence_num = 0;
    header.data_control = 0;
    header.message_properties = 0;
    header.command_code = 0;
}
 
void Jaus_neighbor::startBroadcasting()
{
 
}
 
void Jaus_neighbor::stopBroadcasting()
{
 
}
 
void Jaus_neighbor::sendDatagram()
{
    //udpSocket->writeDatagram(message, QHostAddress::LocalHost, 9000);
}
 
 
void Jaus_neighbor::handshake()
{
    Jaus_neighbor::startBroadcasting();
}
 
void Jaus_neighbor::prepare_header(){}
void Jaus_neighbor::read_jheader(){}
void Jaus_neighbor::send_jheader(){}
void Jaus_neighbor::do_command(){}

#include "jaus.h"

Jaus_neighbor::Jaus_neighbor()
{
    udpSocket = new QUdpSocket(this);
    for (int i = 0; i < 4; i++)
    {
        header.dest_id[i] = 0;
        header.source_id[i] = 0;
    }
    header.sequence_num = 0;
    header.data_control = 0;
    header.message_properties = 0;
    header.command_code = 0;
}

void Jaus_neighbor::startBroadcasting()
{

}

void Jaus_neighbor::stopBroadcasting()
{

}

void Jaus_neighbor::sendDatagram()
{
    //udpSocket->writeDatagram(message, QHostAddress::LocalHost, 9000);
}


void Jaus_neighbor::handshake()
{
    Jaus_neighbor::startBroadcasting();
}

void Jaus_neighbor::prepare_header(){}
void Jaus_neighbor::read_jheader(){}
void Jaus_neighbor::send_jheader(){}
void Jaus_neighbor::do_command(){}

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Same error though