fatal error LNK1169: one or more multiply defined symbols found in game programming

Question

I've been training to use object orientated programming in c++ but I keep getting this error:

1>main.obj : error LNK2005: "int WIDTH" (?WIDTH@@3HA) already defined in GameObject.obj 1>main.obj : error LNK2005: "int HEIGHT" (?HEIGHT@@3HA) already defined in GameObject.obj 1>Spaceship.obj : error LNK2005: "int WIDTH" (?WIDTH@@3HA) already defined in GameObject.obj 1>Spaceship.obj : error LNK2005: "int HEIGHT" (?HEIGHT@@3HA) already defined in GameObject.obj 1>C:\Users\ted\documents\visual studio 2010\Projects\fullSpace\Debug\fullSpace.exe : fatal error LNK1169: one or more multiply defined symbols found 

However to me, it seems that the entire code is written properly and the two ints are only mentioned in the Global header and all objects seem to be inheriting properly. However, like I just said, I'm a beginner in OOP so I really need an opinion : It is also worth mentioning that I am using allegro 5 to create a side shooter.

This is the code :

(main):

#include <allegro5/allegro.h> #include <allegro5/allegro_image.h> #include <allegro5/allegro_primitives.h> #include <allegro5/allegro_font.h> #include <allegro5\allegro_ttf.h> #include <allegro5\allegro_audio.h> #include <allegro5\allegro_acodec.h>  #include <list>   #include "GameObject.h" #include "Spaceship.h" #include "Globals.h"    //controls  bool keys[] = {false, false, false, false, false}; enum KEYS{UP, DOWN, LEFT, RIGHT, SPACE};  //globals Spaceship *ship;  std::list <GameObject *> objects; std::list <GameObject *>::iterator iter; std::list <GameObject *>::iterator iter2;    //prototypes    //main function int main(int argc, char **argv) {     //shell variables     bool done = false;     bool render = false;      float gameTime = 0;     int frames = 0;     int gameFPS = 0;      //project variables      ship = new Spaceship();       ALLEGRO_BITMAP *shipImage = NULL;     ALLEGRO_BITMAP *cometImage= NULL;     ALLEGRO_BITMAP *explImage = NULL;     ALLEGRO_BITMAP *bgImage = NULL;     ALLEGRO_BITMAP *mgImage = NULL;     ALLEGRO_BITMAP *plImage = NULL;     ALLEGRO_BITMAP *mgImage2 = NULL;     ALLEGRO_BITMAP *fgImage = NULL;     ALLEGRO_BITMAP *titleImage= NULL;     ALLEGRO_BITMAP *lostImage = NULL;       //allegro variables     ALLEGRO_DISPLAY *display = NULL;     ALLEGRO_EVENT_QUEUE *event_queue = NULL;     ALLEGRO_TIMER *timer;     ALLEGRO_FONT *font18;        //initiate variables     if(!al_init())         return -1;      display = al_create_display(WIDTH, HEIGHT);     if(!display)     return -1;      //addon installation      al_install_keyboard();     al_init_image_addon();     al_init_font_addon();     al_init_ttf_addon();     al_init_primitives_addon();     al_install_audio();     al_init_acodec_addon();      //project init      font18 = al_load_font("arial.ttf", 18, 0);     al_reserve_samples(15);         bgImage = al_load_bitmap("layer1.png");     mgImage = al_load_bitmap("layer2.png");     plImage = al_load_bitmap("starMG.png");     mgImage2 = al_load_bitmap("layer3.png");     fgImage = al_load_bitmap("layer4.png");         shipImage = al_load_bitmap("spaceship.png");     al_convert_mask_to_alpha(shipImage, al_map_rgb(255, 0, 255));        cometImage = al_load_bitmap("asteroid-1-96.png");     explImage = al_load_bitmap("explosion_3_40_128.png");      titleImage = al_load_bitmap("Shooter_Title.png");     lostImage = al_load_bitmap("Shooter_Lose.png");        //object init     ship->init(shipImage);       //iter list     objects.push_back(ship);       srand(time(NULL));      //timer init and startup      event_queue = al_create_event_queue();     timer = al_create_timer(1.0 / 60);      al_register_event_source(event_queue, al_get_timer_event_source(timer));     al_register_event_source(event_queue, al_get_keyboard_event_source());      al_start_timer(timer);     gameTime = al_current_time();      while(!done)     {         ALLEGRO_EVENT ev;         al_wait_for_event(event_queue, &ev);          //input         if(ev.type == ALLEGRO_EVENT_KEY_DOWN)         {             switch(ev.keyboard.keycode)             {             case ALLEGRO_KEY_ESCAPE:                 done = true;                 break;             case ALLEGRO_KEY_LEFT:                 keys[LEFT] = true;                 break;             case ALLEGRO_KEY_RIGHT:                 keys[RIGHT] = true;                 break;             case ALLEGRO_KEY_UP:                 keys[UP] = true;                 break;             case ALLEGRO_KEY_DOWN:                 keys[DOWN] = true;                 break;             case ALLEGRO_KEY_SPACE:                 keys[SPACE] = true;                 break;               }         } else if(ev.type == ALLEGRO_EVENT_KEY_UP)         {             switch(ev.keyboard.keycode)             {             case ALLEGRO_KEY_ESCAPE:                 done = true;                 break;             case ALLEGRO_KEY_LEFT:                 keys[LEFT] = false;                 break;             case ALLEGRO_KEY_RIGHT:                 keys[RIGHT] = false;                 break;             case ALLEGRO_KEY_UP:                 keys[UP] = false;                 break;             case ALLEGRO_KEY_DOWN:                 keys[DOWN] = false;                 break;             case ALLEGRO_KEY_SPACE:                 keys[SPACE] = false;                 break;             }         }            else if (ev.type == ALLEGRO_EVENT_TIMER)         {             render = true;              //fps             frames++;             if(al_current_time() - gameTime >= 1)             {                 gameTime = al_current_time();                 gameFPS = frames;                 frames = 0;             }              //shipUpdate              if(keys[UP])                 ship ->moveUp();             else if(keys[DOWN])                 ship ->moveDown();             else                 ship->resetAnim(1);              if(keys[LEFT])                 ship ->moveLeft();             else if(keys[RIGHT])                 ship -> moveRight();             else                 ship ->resetAnim(0);          }         //render              if(render && al_is_event_queue_empty(event_queue))             {                 render = false;                  //begin render                 for(iter = objects.begin(); iter != objects.end(); ++iter)                     (*iter)->render();                     //Flip Buffers                 al_flip_display();                 al_clear_to_color(al_map_rgb(0,0,0));             }         }                  //destroy objects            //visual objects     al_destroy_bitmap(cometImage);     for(iter = objects.begin(); iter != objects.end(); ++iter)         (*iter)->destroy(shipImage);         iter = objects.erase(iter);      al_destroy_bitmap(explImage);     al_destroy_bitmap(bgImage);     al_destroy_bitmap(mgImage);     al_destroy_bitmap(fgImage);     al_destroy_bitmap(titleImage);     al_destroy_bitmap(lostImage);          //audio objects     /*     al_destroy_sample(shot);     al_destroy_sample(boom);     al_destroy_sample(song);     al_destroy_sample_instance(songInstance);     */           //shell objects     al_destroy_font(font18);     al_destroy_timer(timer);     al_destroy_event_queue(event_queue);     al_destroy_display(display);      return 0; } 

(Globals.h):

#pragma once  int WIDTH = 1024; int HEIGHT = 800;  enum ID{PLAYER, ENEMY, BULLET, BORDER, MISC}; enum STATES{TITLE, PLAYING, LOST}; 

(GameObject.h):

#pragma once   #include "Globals.h" #include <iostream>  #include <allegro5/allegro5.h>  #include <allegro5/allegro_primitives.h>    class GameObject { private:     int ID;     bool alive;     bool collidable;  protected:     float x;     float y;      float velX;     float velY;      int dirX;     int dirY;      int boundX;     int boundY;      int maxFrame;     int curFrame;     int frameCount;     int frameDelay;     int frameWidth;     int frameHeight;     int animationColumns;     int animationDirection;      ALLEGRO_BITMAP *image;  public:     GameObject();     void virtual destroy(ALLEGRO_BITMAP *image);      void init(float x, float y, float velX, float velY, int dirX, int dirY, int boundX, int boundY);     void virtual update();     void virtual render();      float getX() {return x;}     float getY() {return y;}      void setX(float x) {GameObject::x = x;}     void setY(float y) {GameObject::y = y;}      int getBoundX() {return boundX;}     int getBoundY() {return boundY;}      int getID() {return ID;}     void setID(int ID) {GameObject::ID = ID;}      bool getAlive() {return alive;}     void setAlive(bool alive) {GameObject::alive = alive;}      bool getCollidable() {return collidable;}     void setCollidable(bool collidable) {GameObject::collidable = collidable;}      bool checkCollisions(GameObject *otherObject);     void virtual collided(int objectID);     bool collidableCheck(); }; 

(GameObject.cpp):

#include "GameObject.h"  GameObject::GameObject() {     x = 0;     y = 0;      velX = 0;     velY = 0;      dirX = 0;     dirY = 0;      boundX = 0;     boundY = 0;      maxFrame = 0;     curFrame = 0;     frameCount = 0;     frameDelay = 0;     frameWidth = 0;     frameHeight = 0;     animationColumns = 0;     animationDirection = 0;      image = NULL;      alive = true;     collidable = true;  }  void GameObject::destroy(ALLEGRO_BITMAP *image) {     if(image != NULL)         al_destroy_bitmap(image);  } void GameObject::init(float x, float y, float velX, float velY, int dirX, int dirY, int boundX, int boundY) {     GameObject::x = x;     GameObject::y = y;      GameObject::velX = velX;     GameObject::velY = velY;      GameObject::dirX = dirX;     GameObject::dirY = dirY;      GameObject::boundX = boundX;     GameObject::boundY = boundY;  }  void GameObject::update() {     x += velX*dirX;     y += velY*dirY; }  void GameObject::render() {  }  bool GameObject::checkCollisions(GameObject *otherObject) {     float oX = otherObject->getX();     float oY = otherObject->getY();      int obX = otherObject->getBoundX();     int obY = otherObject->getBoundY();      if(x + boundX > oX - obX &&        x - boundX < oX + obX &&        y + boundY > oY - obY &&        y - boundY < oY + obY        )        return true;     else        return false; }  void GameObject::collided(int objectID) {  } bool GameObject::collidableCheck() {     return alive && collidable; } 

(SpaceShip.h):

#pragma once  #include "GameObject.h"  class Spaceship : public GameObject { private :     int lives;     int score;     int animationRow;  public :     Spaceship();      void destroy(ALLEGRO_BITMAP *image);      void init(ALLEGRO_BITMAP *image = NULL);      void update();     void render();      void moveUp();     void moveDown();     void moveLeft();     void moveRight();      void resetAnim(int pos);      int getLives(){return lives;}      int getScore() {return score;}      void looseLife() {lives--;}     void addPoint() {score++;}      void collide(int objectID);    }; 

(SpaceShip.cpp):

#include "Spaceship.h"      Spaceship::Spaceship()     {}      void Spaceship::destroy(ALLEGRO_BITMAP *image)     {         GameObject::destroy(image);     }     void Spaceship::init(ALLEGRO_BITMAP *image)     {         GameObject::init(20, 200, 6, 6, 0, 0, 10, 12);          setID(PLAYER);         setAlive(true);          lives = 3;         score = 0;          maxFrame = 3;         curFrame = 0;         frameWidth = 46;         frameHeight = 41;         animationColumns = 3;         animationDirection = 1;          animationRow = 1;          if(image != NULL)         {             Spaceship::image = image;         }     }      void Spaceship::update()     {         GameObject::update();         if(x < 0)             x=0;         else if ( x > WIDTH)             x = WIDTH;         if(y < 0)             y = 0;         else if (y > HEIGHT)             y = HEIGHT;     }     void Spaceship::render()     {         GameObject::render();          int fx = (curFrame % animationColumns) *frameWidth;         int fy = animationRow *frameHeight;          al_draw_bitmap_region(image, fx, fy, frameWidth, frameHeight,             x - frameWidth /2, y - frameHeight /2, 0);      }      void Spaceship::moveUp()     {         animationRow = 0;         dirY = -1;      }     void Spaceship::moveDown()     {         animationRow = 2;         dirY = 1;     }     void Spaceship::moveLeft()     {         curFrame = 2;         dirX = -1;     }     void Spaceship::moveRight()     {         curFrame = 1;         dirX = 1;     }      void Spaceship::resetAnim(int pos)     {         if(pos == 1)         {             animationRow = 1;             dirY = 0;         }         else         {             curFrame = 0;             dirX = 0;         }     }      void Spaceship::collide(int objectID)     {         if(objectID == ENEMY)             lives--;      } 

Answer 1

The two int variables are defined in the header file. This means that every source file which includes the header will contain their definition (header inclusion is purely textual). The of course leads to multiple definition errors.

You have several options to fix this.

1. Make the variables static (static int WIDTH = 1024;). They will still exist in each source file, but their definitions will not be visible outside of the source file.

2. Turn their definitions into declarations by using extern (extern int WIDTH;) and put the definition into one source file: int WIDTH = 1024;.

3. Probably the best option: make the variables const (const int WIDTH = 1024;). This makes them static implicitly, and also allows them to be used as compile-time constants, allowing the compiler to use their value directly instead of issuing code to read it from the variable etc.

Answer 2

You can't put variable definitions in header files, as these will then be a part of all source file you include the header into.

The #pragma once is just to protect against multiple inclusions in the same source file, not against multiple inclusions in multiple source files.

You could declare the variables as extern in the header file, and then define them in a single source file. Or you could declare the variables as const in the header file and then the compiler and linker will manage it.