Leandro Oliveira Rezende Leandro Oliveira Rezende - 17 days ago 7
C++ Question

Undefined reference to vtable with nested class

When I try to compile the following code:

Alien::Action::Action(ActionType type, float x, float y) {
Action::type = type;
pos = Vec2(x, y);
}

Alien::Alien(float x, float y, int nMinions) {
srand(time(NULL));
sp = Sprite("img/alien.png");
box = Rect(x, y, sp.GetWidth(), sp.GetHeight());
box.x = x - box.h/2;
box.y = y - box.w/2;
hitpoints = 100;
speed.x = 0.5;
speed.y = 0.5;
minionArray = std::vector<Minion>();
for(int i = 0; i < nMinions; i++) {
int a = rand()%501;
float b = a/1000.0;
float c = b+1;
minionArray.emplace_back(Minion(get(), i*(360/nMinions), c));
}
taskQueue = std::queue<Action>();
}


The IDE (Eclipse) gives the following error message: "undefined reference to 'vtable for Alien'" (line 6 of the code). Since there's no virtual method inside Alien, I don't know the cause of the error. The following is the header file for Alien:

#ifndef ALIEN_H_
#define ALIEN_H_

#include "GameObject.h"

class Alien: public GameObject {
private:
class Action {
public:
enum ActionType {MOVE, SHOOT};
ActionType type;
Action(ActionType type, float x, float y);
Vec2 pos;
};
int hitpoints;
std::queue<Action> taskQueue;
std::vector<Minion> minionArray;
public:
Alien(float x, float y, int nMinions);
~Alien();
void Update(float dt);
void Render();
Alien* get();
bool IsDead();
};

#endif


The code for GameObject is :

#include "GameObject.h"
#include "InputManager.h"
#include "Camera.h"
#include "State.h"

GameObject::~GameObject() {

}

GameObject* GameObject::get() {
return this;
}

Minion::~Minion() {

}

Minion::Minion(GameObject* minionCenter, float arcOffset, float minionSize) {
sp = Sprite("img/minion.png");
center = minionCenter;
translation = arcOffset;
box = Rect(center->box.GetCenter().x+(cos(translation*M_PI/180)*200)-(sp.GetWidth()/2),
center->box.GetCenter().y+(sin(translation*M_PI/180)*200)-(sp.GetHeight()/2),
sp.GetWidth(), sp.GetHeight());
}

void Minion::Shoot(Vec2 pos) {
State::AddObject(new BulletWheel(box.GetCenter().x, box.GetCenter().y, center->box.GetCenter().GetDX(pos.x),
center->box.GetCenter().GetDY(pos.y), center->box.GetCenter().GetDS(pos), 0.3,
translation, center->box.GetCenter(), "img/minionbullet1.png"));
}

void Minion::Update(float dt) {
if(translation < 360)
translation += 0.03*dt;
else
translation += 0.03*dt-360;
/*rotation = translation-90;*/
if(rotation < 360)
rotation += 0.15*dt;
else
rotation += 0.15*dt-360;
box.x = center->box.GetCenter().x+(200*cos((translation)*M_PI/180))-(box.w/2);
box.y = center->box.GetCenter().y+(200*sin((translation)*M_PI/180))-(box.h/2);
}

void Minion::Render() {
sp.Render(box.x - Camera::GetInstance().pos.x, box.y - Camera::GetInstance().pos.y, rotation);
}

bool Minion::IsDead() {
return false;
}

Bullet::Bullet(float x, float y, float dx, float dy, float maxDistance, float speed, std::string sprite) {
sp = Sprite(sprite);
box = Rect(x-(sp.GetWidth()/2), y-(sp.GetHeight()/2), sp.GetWidth(), sp.GetHeight());
Bullet::speed = Vec2(speed*(dx/maxDistance), speed*(dy/maxDistance));
distanceLeft = maxDistance;
rotation = atan2(dy, dx)*(180/M_PI);
}

void Bullet::Update(float dt) {
if(distanceLeft > 0) {
box.x += speed.x*dt;
box.y += speed.y*dt;
distanceLeft -= pow(pow(speed.x*dt,2)+pow(speed.y*dt,2),0.5);
}
}

void Bullet::Render() {
sp.Render(box.x - Camera::GetInstance().pos.x, box.y - Camera::GetInstance().pos.y, rotation);
}

bool Bullet::IsDead() {
return (distanceLeft < 1) ? true : false;
}

Bullet* Bullet::get() {
return this;
}

BulletWheel::BulletWheel(float x, float y, float dx, float dy, float maxDistance, float speed, float arcOffset, Vec2 center, std::string sprite) {
sp = Sprite(sprite);
sp.SetScaleX(2);
sp.SetScaleY(2);
box = Rect(x-(sp.GetWidth()/2), y-(sp.GetHeight()/2), sp.GetWidth(), sp.GetHeight());
BulletWheel::speed = Vec2(speed*(dx/maxDistance), speed*(dy/maxDistance));
distanceLeft = maxDistance;
rotation = atan2(dy, dx)*(180/M_PI);
translation = arcOffset;
BulletWheel::center = center;
}

void BulletWheel::Update(float dt) {
if(translation < 360)
translation += 0.1*dt;
else
translation += 0.1*dt-360;
if(distanceLeft > 0.01) {
center.x += speed.x*dt;
center.y += speed.y*dt;
box.x = center.x+(200*cos((translation)*M_PI/180))-(box.w/2);
box.y = center.y+(200*sin((translation)*M_PI/180))-(box.h/2);
distanceLeft -= pow(pow(speed.x*dt,2)+pow(speed.y*dt,2),0.5);
}
}

void BulletWheel::Render() {
sp.Render(box.x - Camera::GetInstance().pos.x, box.y - Camera::GetInstance().pos.y, rotation);
}

bool BulletWheel::IsDead() {
return distanceLeft < 1;
}

BulletWheel* BulletWheel::get() {
return this;
}


and its header file is:
#ifndef GAMEOBJECT_H_
#define GAMEOBJECT_H_

#include "Sprite.h"
#include "Rect.h"
#include "Vec2.h"
#include <queue>
#include <vector>
#include <cmath>
#include <ctime>

class GameObject{
private:

public:
virtual ~GameObject();
virtual void Update(float dt) = 0;
virtual void Render() = 0;
virtual bool IsDead() = 0;
virtual GameObject* get();
int rotation = 0;
int translation = 0;
Sprite sp = Sprite();
Vec2 speed = Vec2();
Rect box = Rect();
};

class Minion : public GameObject {
private:
GameObject* center;

public:
Minion(GameObject* minionCenter, float arcOffset, float minionSize = 1);
~Minion();
void Shoot(Vec2 pos);
void Update(float dt);
void Render();
bool IsDead();
Minion* get();
};

class Bullet : public GameObject {
private:
float distanceLeft;
public:
Bullet(float x, float y, float dx, float dy, float maxDistance, float speed, std::string sprite);
void Update(float dt);
void Render();
bool IsDead();
Bullet* get();
};

class BulletWheel : public GameObject {
private:
float distanceLeft;
Vec2 center;
public:
BulletWheel(float x, float y, float dx, float dy, float maxDistance, float speed, float arcOffset, Vec2 center, std::string sprite);
void Update(float dt);
void Render();
bool IsDead();
BulletWheel* get();
};

#endif /* GAMEOBJECT_H_ */


There are the virtual functions of GameObject, declared inside Alien.cpp:

void Alien::Update(float dt) {
if(rotation > 0)
rotation -= 0.1*dt;
else
rotation -= 0.1*dt+360;
if(InputManager::GetInstance().MousePress(RIGHT_MOUSE_BUTTON)) {
taskQueue.push(Action(Action::MOVE,(InputManager::GetInstance().GetMouseX() + Camera::GetInstance().pos.x - (box.w/2)),
(InputManager::GetInstance().GetMouseY() + Camera::GetInstance().pos.y - (box.h/2))));
}
if(InputManager::GetInstance().MousePress(LEFT_MOUSE_BUTTON)) {
taskQueue.push(Action(Action::SHOOT,(InputManager::GetInstance().GetMouseX() + Camera::GetInstance().pos.x),
(InputManager::GetInstance().GetMouseY() + Camera::GetInstance().pos.y)));
}
if(taskQueue.size() > 0) {
Vec2 pos = taskQueue.front().pos;
if(taskQueue.front().type == Action::MOVE) {
float cos = (box.GetDX(pos.x)/box.GetDS(pos));
float sin = (box.GetDY(pos.y)/box.GetDS(pos));
if(cos != cos) {
cos = 0;
}
if(sin != sin) {
sin = 0;
}
if((box.x+speed.x*cos*dt > pos.x && pos.x > box.x) || (box.x+speed.x*cos*dt < pos.x && pos.x < box.x)) {
box.x = pos.x;
}
else {
box.x += speed.x*cos*dt;
}
if((box.y+speed.y*sin*dt > pos.y && pos.y > box.y) || (box.y+speed.y*sin*dt < pos.y && pos.y < box.y)) {
box.y = pos.y;
}
else {
box.y += speed.y*sin*dt;
}
if(box.x == pos.x && box.y == pos.y) {
taskQueue.pop();
}
}
else {
for(unsigned i = 0; i < minionArray.size(); i++) {
minionArray.at(i).Shoot(pos);
taskQueue.pop();
}
}
}
for(unsigned i = 0; i < minionArray.size(); i++) {
minionArray.at(i).Update(dt);
}
}

void Alien::Render() {
sp.Render(box.x - Camera::GetInstance().pos.x, box.y - Camera::GetInstance().pos.y, rotation);
if(minionArray.size() > 0) {
for(unsigned i = 0; i < Alien::minionArray.size(); i++) {
minionArray.at(i).Render();
}
}
}

bool Alien::IsDead() {
return (Alien::hitpoints <= 0);
}


EDIT: the destructor of Alien was missing.

Answer

All classes derived from GameObject must define all pure virtual functions in GameObject. In your case, this is:

virtual void Update(float dt) = 0;
virtual void Render() = 0;
virtual bool IsDead() = 0;

Here is a similar question with more information. Hope this helps!