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 gt main obj   error LNK2005   int WIDTH    WIDTH  3HA  already defined in GameObject obj 1 gt main obj   error LNK2005   int HEIGHT    HEIGHT  3HA  already defined in GameObject obj 1 gt Spaceship obj   error LNK2005   int WIDTH    WIDTH  3HA  already defined in GameObject obj 1 gt Spaceship obj   error LNK2005   int HEIGHT    HEIGHT  3HA  already defined in GameObject obj 1 gt 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  lt allegro5 allegro h gt   include  lt allegro5 allegro image h gt   include  lt allegro5 allegro primitives h gt   include  lt allegro5 allegro font h gt   include  lt allegro5 allegro ttf h gt   include  lt allegro5 allegro audio h gt   include  lt allegro5 allegro acodec h gt    include  lt list gt     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  lt GameObject   gt  objects  std  list  lt GameObject   gt   iterator iter  std  list  lt GameObject   gt   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- gt 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   amp 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  gt   1                                gameTime   al current time                    gameFPS   frames                  frames   0                               shipUpdate              if keys UP                   ship - gt moveUp                else if keys DOWN                   ship - gt moveDown                else                 ship- gt resetAnim 1                if keys LEFT                   ship - gt moveLeft                else if keys RIGHT                   ship - gt  moveRight                else                 ship - gt resetAnim 0                        render              if render  amp  amp  al is event queue empty event queue                                 render   false                     begin render                 for iter   objects begin    iter    objects end      iter                        iter - gt 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 - gt 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  lt iostream gt    include  lt allegro5 allegro5 h gt    include  lt allegro5 allegro primitives h gt     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- gt getX        float oY   otherObject- gt getY         int obX   otherObject- gt getBoundX        int obY   otherObject- gt getBoundY         if x   boundX  gt  oX - obX  amp  amp         x - boundX  lt  oX   obX  amp  amp         y   boundY  gt  oY - obY  amp  amp         y - boundY  lt  oY   obY                 return true      else        return false     void GameObject  collided int objectID       bool GameObject  collidableCheck         return alive  amp  amp  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  lt  0              x 0          else if   x  gt  WIDTH              x   WIDTH          if y  lt  0              y   0          else if  y  gt  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--

User · Answer

just add  FORCE as linker flag and you re all set    for instance  if you re working on CMakeLists txt  Then add following line    SET CMAKE EXE LINKER FLAGS    FORCE

User · Answer

const int WIDTH   1024  const int HEIGHT   800

User · Answer

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

User · Answer

I answered a similar question here  In the Project   s Settings  add   FORCE MULTIPLE to the Linker   s Command Line options  From MSDN   quot Use  FORCE MULTIPLE to create an output file whether or not LINK finds more than one definition for a symbol  quot  That s what programmers call a  quot quick and dirty quot  solution  but sometimes you just want the build to be completed and get to the bottom of the problem later  so that s kind of a ad-hoc solution  To actually avoid this error  provided that you want int WIDTH   1024  int HEIGHT   800   to be shared among several source files  just declare them only in a single  c    cpp file  and refer to them in a header file  extern int WIDTH  extern int HEIGHT   Then include the header in any other source file you wish these global variables to be available

User · Answer

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    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  Turn their definitions into declarations by using extern  extern int WIDTH   and put the definition into one source file  int WIDTH   1024   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

[c++] fatal error LNK1169: one or more multiply defined symbols found in game programming

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