Multiple Definitions in C++ (Visual Basic 2010)

Question

I'm attempting to practice some coding in my free time (combining a number of different interests of mine to help keep myself engaged) and I've encountered a odd error that I can't find the answer to. I have 4 files that I'm working with, two header files, one class definition file and a main file. I'm fairly confident I'm not including the Dice.h file more then once (however that is where the error points to and I'm not sure anymore, hence this question). What have I bungled here to produce these errors?

The error codes

Error 3 error LNK1169: one or more multiply defined symbols found (file path trimmed)

Error 2 error LNK2005: "int __cdecl dice(int,int)" (?dice@@YAHHH@Z) already defined in Creature.obj (file path trimmed)

The filepath: c:\Users\Username\documents\visual studio2010\Projects\RPGTest\RPGTest\RPGTest.(error 3 referenced a .exe file, error 2 referenced a .obj file).

The code itself:

Dice.h

#ifndef SET_DICE_H_
#define SET_DICE_H_

#include <iomanip>
#include <iostream>
#include <stdlib.h>

using namespace std;

int dice(int number, int sides){

int total=0, dice;
srand(time(NULL));
int results=0;
do {
    dice = rand()%sides+1;
    total+=dice;
    number--;
} while (number > 0);
results = total;
return results;
}
#endif

Creature.h

#ifndef CREATURE_H_
#define CREATURE_H_

#include <iomanip>
#include <iostream>
#include "Dice.h"
using namespace std;

class Creature {
public:
    Creature(int,int,int,int,int,int,int,int,int,int,int,int);
    void set_hp();
    void set_saves();
    void set_ac();
    void set_bab();
    void set_name();
    void update_hp(int);
    void update_ac(int);
    void update_fsave(int);
    void update_rsave(int);
    void update_wsave(int);
    int get_ac();
    int get_hp();
    int get_fsave();
    int get_rsave();
    int get_wsave();
    int get_bonus(int);
    int get_bab();
    string get_name();
private:
    int strength, dexterity, constitution, intellegence, wisdom, charisma;
    int bab, fbsave, rbsave, wbsave;
    int hdnum, hdsize;
    int hp, fsave, rsave, wsave, ac;
    string name;

};
#endif

Creature.cpp

#include "Creature.h"
#include <math.h>
#include <iostream>

using namespace std;

Creature::Creature(int strength,int dexterity,int constitution,
    int intellegence,int wisdom,int charisma,int bab,int fbsave,
    int rbsave,int wbsave,int hdnum,int hdsize){
        strength = strength;
        dexterity = dexterity;
        constitution = constitution;
        intellegence = intellegence;
        wisdom = wisdom;
        charisma = charisma;
        bab = bab;
        fbsave = fbsave;
        rbsave = rbsave;
        wbsave = wbsave;
        hdnum = hdnum;
        hdsize = hdsize;
}

int Creature::get_bonus(int stat){
    int bonus = floor((double(stat)-10)/2);
    return bonus;
}

void Creature::set_ac(){
    ac=10+get_bonus(dexterity);
}

void Creature::set_hp(){
    hp = dice(hdnum,hdsize) + get_bonus(constitution)*hdnum;
}

void Creature::set_saves(){
    fsave = fbsave + get_bonus(constitution);
    rsave = rbsave + get_bonus(dexterity);
    wsave = wbsave + get_bonus(wisdom);
}

void Creature::set_bab(){
    bab = hdnum;
}

void Creature::set_name(){
    cout << "Please enter a name for this creature: ";
    cout << "\nSorry! I don't work yet!";
    cout << "\nInstead all creatures are named Larry!\n";
    name = "Larry!";
}

void Creature::update_hp(int input){
    hp = hp + input;
}

void Creature::update_fsave(int input){
    fsave = fsave+input;
}

void Creature::update_rsave(int input){
    rsave = rsave+input;
}

void Creature::update_wsave(int input){
    wsave = wsave+input;
}

void Creature::update_ac(int input){
    ac = ac+input;
}

int Creature::get_ac(){
    return ac;
}

int Creature::get_hp(){
    return hp;
}

int Creature::get_fsave(){
    return fsave;
}

int Creature::get_rsave(){
    return rsave;
}

int Creature::get_wsave(){
    return wsave;
}

int Creature::get_bab(){
    return bab;
}

RPGTest.cpp

#include "Creature.h"
#include <math.h>
//#include "Dice.h"
#include <iostream>
#include <iomanip>

using namespace std;

int main(){

    int str = dice(3,6), dex = dice(3,6), con = dice(3,6), intel = dice(3,6), wis = dice(3,6), cha = dice(3,6);
    int fbs = dice(1,6), rbs = dice(1,6), wbs = dice(1,6);
    int hdn = dice(1,10), hds = 8, bab = dice(1,8);

    cout << "Welcome to RPG Creature Tester v0.1\n";
    cout << "This .exe file is meant to test the creature class functions and definitions.\n";
    cout << "This will be done by randomly generating and displaying a creature.\n";
    cout << "What you don't see right now is the random generation of a creature.\n";
    cout << "Once it's finished, the \'statsheet\' will be shown.\n";
    cout << "Cheers!\n\n";

    Creature potato (str, dex, con, intel, wis, cha, bab, fbs, rbs, wbs, hdn, hds);

    potato.set_ac();
    potato.set_hp();
    potato.set_name();
    potato.set_saves();

    cout << "OUTPUT BRICK YAY\n";
    cout << "Str: " << str << endl;
    cout << "HP: " << potato.get_hp() << " AC: " << potato.get_ac() << " Fort/Reflex/Will Save: " << potato.get_fsave() << "/" << potato.get_rsave() << "/" << potato.get_wsave();

    return 0;
}

Since I'm mainly self-taught I'm happy for any other advice but my main issue is that I'm not sure why I'm getting the "multiple" definition error. I did some research into other questions with similar error messages but I didn't see anything that immediately jumped out at me as "the answer".

Thanks all!

Answer 1

C++ works by compiling single translation units and then linking them together.

This means that each source file gets compiled on its own. Since the #include directive basically inserts all the code included, in your situation you end up having multiple translation units which define

int dice(int number, int sides) {
  ...
}

Compilation goes through fine but, when linking, multiple definition of this function are found so this generates the error.

To solve this problem you have two ways:

• declare int dice(int, int) in a header file but define (implement it) in a source file
• keep the definition as it is but prepend static to it. This tells the compiler that each translation unit will get its own dice method. This solution, although tempting, leads to binary size increase since you will have multiple implementation of the same method