can't find linker symbol for virtual table for `Controller' value

maxp

Re: Can't find linker symbol for virtual table

Hi, the linker symbol problem as mentioned in the topic above still seems to be present?

I made a small code example with which I keep on having the notification "can't find linker symbol for virtual table for 'Controller' value" in QtCreator while running the application in debug mode and having a breakpoint on "Controller controller;". Even after doing a fresh clean, qmake and build.

Platform: Windows 10
IDE: QtCreator version 4.11.1 (Built on Feb 5 2020).
Kit: Desktop Qt 5.12.6 MinGW 32-bit

#include "Controller.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Controller controller;                   // Put breakpoint here
    return a.exec();
}

// Controller.h
#ifndef CONTROLLER_H
#define CONTROLLER_H

#include "MainWindow.h"
#include <QObject>

class Controller : public QObject
{
    Q_OBJECT

public:
    Controller(QObject *parent = nullptr);
    ~Controller();

private:
    MainWindow *m_mainWindow;
};
#endif // CONTROLLER_H

// Controller.cpp
#include "Controller.h"

Controller::Controller(QObject* parent)
    : QObject(parent)
    //, m_mainWindow(new MainWindow())  // Virtual table notification occurs no matter if this line is commented or not
{
}

Controller::~Controller()
{
}

// MainWindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
};
#endif // MAINWINDOW_H

// MainWindow.cpp
#include "MainWindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
}

MainWindow::~MainWindow()
{
}

So, I got these virtual table notifications in debug mode in a larger program. I then created a completely new Qt Widgets Application and just added the Controller class in between. Initializing the m_mainWindow pointer or not and cleaning it up in the example does not change anything for the notification. Am I missing anything here or is there some problem with QtCreator or so?

With kind regards

maxp

Pro file

QT       += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
CONFIG += c++11
DEFINES += QT_DEPRECATED_WARNINGS

SOURCES += \
    main.cpp \
    Controller.cpp \
    MainWindow.cpp

HEADERS += \
    Controller.h \
    MainWindow.h

maxp

The notification is not shown in the following cases:

when building the same code with MinGW 64-bit (instead of the 32-bit)
when adding controller.setObjectName("Controller");
using Controller *controller = new Controller(); and deleting it at the end

kshegunov

@maxp said in can't find linker symbol for virtual table for `Controller' value:

when building the same code with MinGW 64-bit (instead of the 32-bit)

Then probably doesn't mean anything. Does your code run correctly otherwise?

maxp

Thanks for answering. Yes, I haven't spot any problems yet with running apart from that notification.
But since I get it here on several Windows computers, I wanted to be sure.

kshegunov

Well, my best advice is keep an eye on it, if it causes trouble in the future then revisit the issue. I couldn't spot anything obvious in the code itself, and it disappearing with a different version of the same compiler probably means it's some peculiarity of the linkage that's probably irrelevant.