error: undefined reference to

Question

I made a Player class which inherits from Controller class. It's a class for controlling a unit in a game. I get this error with it:

error: undefined reference to 'Controller::Controller()'

I'm not sure what i'm doing wrong here. Does anyone know what goes wrong?

Thanks

This is the code:

controller.h

#ifndef CONTROLLER_H
#define CONTROLLER_H

class Controller;

#include <qDebug>

class Controller
{
public:
    Controller();

    virtual bool w();
    virtual bool a();
    virtual bool s();
    virtual bool d();
    virtual bool space();

private:

};

#endif // CONTROLLER_H

player.h

#ifndef PLAYER_H
#define PLAYER_H

class Player;

#include "controller.h"
#include "view/mainwindow.h"

#include <QString>

class Player : public Controller
{
public:
    Player(QString name, MainWindow *window);

    // Controller functions
    bool w();
    bool a();
    bool s();
    bool d();
    bool space();

private:
    QString name;
    MainWindow *window;
};

#endif // PLAYER_H

player.cpp

#include "player.h"

Player::Player(QString name, MainWindow *window) {
    this->name = name;
    this->window = window;
}

bool Player::w() {return window->w();}
bool Player::a() {return window->a();}
bool Player::s() {return window->s();}
bool Player::d() {return window->d();}
bool Player::space() {return window->space();}