LNK2019 unresolved External Symbol for a QObject

Question

I'm getting the following errors when building with QMake:

LNK2019: unresolved external symbol "public: void __cdecl TimerTodo::notify(class TodoBaseTask *)" (?notify@TimerTodo@@QEAAXPEAVTodoBaseTask@@@Z) referenced in function "private: void __cdecl TimerTodo::timerOver(void)" (?timerOver@TimerTodo@@AEAAXXZ)

LNK2019: unresolved external symbol "public: void __cdecl TimerTodo::hasNotified(class TimerTodo *)" (?hasNotified@TimerTodo@@QEAAXPEAV1@@Z) referenced in function "private: void __cdecl TimerTodo::timerOver(void)" (?timerOver@TimerTodo@@AEAAXXZ)

LNK1120: 2 unresolved externals

This is my header:

#ifndef TIMERTODO_H
#define TIMERTODO_H

#include <QTimer>

class TodoBaseTask;

class TimerTodo : public QTimer
{
public:
    TimerTodo(TodoBaseTask *timer);
    void StartTimer();
private slots:
    void timerOver();
signals:
    void notify(TodoBaseTask *todo);
    void hasNotified(TimerTodo *timer);
private:
    TodoBaseTask *m_todo;
};

#endif // TIMERTODO_H

And this is my source:

#include "timertodo.h"
#include "todobasetask.h"

TimerTodo::TimerTodo(TodoBaseTask *todo)
{
    m_todo = todo;
    connect(this, SIGNAL(timeout()), this, SLOT(timerOver()));
}

void TimerTodo::StartTimer()
{
    QDateTime nextNotify = m_todo->getDeadLine().addDays(-1);
    this->start(QDateTime::currentDateTime().msecsTo(nextNotify));
}

void TimerTodo::timerOver()
{
    emit notify(m_todo);
    emit hasNotified(this);
}

How to fix it?

Simply add Q_OBJECT macro in your class declaration and rebuild. — vahancho
Ah yes of course, thank you for helping me out with that one :) — Dennis

BartoszKP BartoszKP · Accepted Answer · 2014-07-28T11:05:56

This is explained in Qt documentation:

The moc tool reads a C++ header file. If it finds one or more class declarations that contain the Q_OBJECT macro, it produces a C++ source file containing the meta-object code for those classes. Among other things, meta-object code is required for the signals and slots mechanism, the run-time type information, and the dynamic property system.

(emphasis mine)

So you need to put this macro in every class that has its own signals or slots.

LNK2019 unresolved External Symbol for a QObject

1 Answers