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LNK1169 error

Dko (1)
Hello,
I've been reading the book "Game Programming All In One. Third Edition" and have been loving the book. But I know C++ better then I know C, so I thought I would convert the books first example of Tank War to C++ classes. Everything worked great till I tried separating the tank/bullet classes I had created out of the main file and into a separate .h/.cpp file.
But now I get the error:
1>tank.obj : error LNK2005: "public: static int tagTank::numTanks" (?numTanks@tagTank@@2HA) already defined in Main.obj
1>tank.obj : error LNK2005: "class tagTank * tanks" (?tanks@@3PAVtagTank@@A) already defined in Main.obj
1>C:\Documents and Settings\Jesse\My Documents\Visual Studio 2010\Projects\Tank Battle\Debug\Tank Battle.exe : fatal error LNK1169: one or more multiply defined symbols found

I have narrowed this down my self to the fact that in my tank.h I end with the code "} tanks[2];" But I can't think of how to change it so I don't get the LNK error. Could anyone give some help as to how to alleviate this problem since I don't know every in and out of C++ classes?

Here is the code I feel is relevant to the problem.
tank.h
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#ifndef _TANK_H
#define _TANK_H

#include "allegro.h"

//constants
const int MAXSPEED = 4;
const int BULLETSPEED = 10;

//define bullet class
class tagBullet
{
public:
    int x,y;
    int alive;
    int xspd,yspd;
    int player;

    int updateBullet();
    int explode(int x, int y);
};

//define tank class
class tagTank
{
public:
    static int numTanks;
    int x,y;
    int dir,speed;
    int color;
    int score;
    int player;
    tagBullet bullet;

    void setupTank();
    void drawTank();
    void eraseTank();
    void moveTank();
    void forward();
    void backward();
    void turnLeft();
    void turnRight();
    void clearPath();
    void fireWeapon();
    
    tagTank()
    { 
        x = 0;
        y = 0;
        dir = 0;
        speed = 0;
        color = 0;
        score = 0;
        player = 0;  // Not a legal player
    };

} tanks[2];

// Initialize instance variable
int tagTank::numTanks = 0;

// Function prototypes
int checkPath(int x1,int y1,int x2,int y2,int x3,int y3);
#endif


main.cpp
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/////////////////////////////////////////////////////////////////////////
// Game Programming All In One, Third Edition
// Chapter 4 - Tank War Game
/////////////////////////////////////////////////////////////////////////

#include "tankbattle.h"
#include "tank.h"




/////////////////////////////////////////////////////////////////////////
// main function
// start point of the program
/////////////////////////////////////////////////////////////////////////
int main(void)
{
    //initialize everything
    allegro_init();  
    install_keyboard(); 
    install_timer();
    srand(time(NULL));
    setupScreen();
    setupDebris();
    tanks[0].setupTank();
    tanks[1].setupTank();

    //game loop
    while(!gameover)
    {
        //erase the tanks
        tanks[0].eraseTank();
        tanks[1].eraseTank();
        
        //check for collisions
        tanks[0].clearPath();
        tanks[1].clearPath();
        
        //move the tanks
        tanks[0].moveTank();
        tanks[1].moveTank();
        
        //draw the tanks
        tanks[0].drawTank();
        tanks[1].drawTank();

        //update the bullets and set score 
        score(tanks[0].bullet.updateBullet());
        score(tanks[1].bullet.updateBullet());
        
        //check for keypresses
        if (keypressed())
            getInput();

        //slow the game down (adjust as necessary)
        rest(30);
    }

    //end program
    allegro_exit();
    return 0;
}
END_OF_MAIN()

/////////////////////////////////////////////////////////////////////////
// getinput function
// check for player input keys (2 player support)
/////////////////////////////////////////////////////////////////////////
void getInput()
{
    //hit ESC to quit
    if (key[KEY_ESC])
        gameover = 1;
    
    //WASD / SPACE keys control tank 1
    if (key[KEY_W])
        tanks[0].forward();
    if (key[KEY_D])
        tanks[0].turnRight();
    if (key[KEY_A])
        tanks[0].turnLeft();
    if (key[KEY_S])
        tanks[0].backward();
    if (key[KEY_SPACE])
        tanks[0].fireWeapon();
            
    //arrow / ENTER keys control tank 2
    if (key[KEY_UP]) 
        tanks[1].forward();
    if (key[KEY_RIGHT])
        tanks[1].turnRight();
    if (key[KEY_DOWN])
        tanks[1].backward();
    if (key[KEY_LEFT])
        tanks[1].turnLeft();
    if (key[KEY_ENTER])
        tanks[1].fireWeapon();

    //short delay after keypress        
    rest(10);
}

/////////////////////////////////////////////////////////////////////////
// score function
// add a point to the specified player's score
/////////////////////////////////////////////////////////////////////////
void score(int player)
{
    if (player != -1)    // Only update score if the player got a hit. 
    {
    //update score
    int points = ++tanks[player].score;

    //display score
    textprintf_ex(screen, font, SCREEN_W-70*(player+1), 1, BURST, 0,
        "P%d: %d", player+1, points);
    }
}


/////////////////////////////////////////////////////////////////////////
// setupdebris function
// set up the debris on the battlefield
/////////////////////////////////////////////////////////////////////////
void setupDebris()
{
    int n,x,y,size,color;

    //fill the battlefield with random debris
    for (n = 0; n < BLOCKS; n++)
    {
        x = BLOCKSIZE + rand() % (SCREEN_W-BLOCKSIZE*2);
        y = BLOCKSIZE + rand() % (SCREEN_H-BLOCKSIZE*2);
        size = (10 + rand() % BLOCKSIZE)/2;
        color = makecol(rand()%255, rand()%255, rand()%255);
        rectfill(screen, x-size, y-size, x+size, y+size, color);
    }

}

/////////////////////////////////////////////////////////////////////////
// setupscreen function
// set up the graphics mode and game screen
/////////////////////////////////////////////////////////////////////////
void setupScreen()
{
    //set video mode    
    int ret = set_gfx_mode(MODE, WIDTH, HEIGHT, 0, 0);
    if (ret != 0) {
        allegro_message(allegro_error);
        return;
    }

    //print title
    textprintf_ex(screen, font, 1, 1, BURST, 0,
        "Tank War - %dx%d", SCREEN_W, SCREEN_H);

    //draw screen border        
    rect(screen, 0, 12, SCREEN_W-1, SCREEN_H-1, TAN);
    rect(screen, 1, 13, SCREEN_W-2, SCREEN_H-2, TAN);
   
}


Also note that everything is public right now until I have everything running right.
Last edited on
Disch (13742)
heh, I just responded to a post with similar troubles.

The problem is you're putting globals in header files. Don't do that.

In fact... try not to use globals at all.

Here's my response to a post with a similar problem:

http://www.cplusplus.com/forum/beginner/28712/#msg155044
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