C++: Multiple definition of object error - c++

Question

I recently started with file structuring in C++ with little success. The project was split into following files
-groups.h
-groups.cpp
-people.h
-people.cpp
-main.cpp
There are 2 base classes, groups and players and every other class in inherited by either of them.
Here's the files
groups.h
people.h
groups.cpp
people.cpp
main.cpp
groups.h
#ifndef GROUPS_H
#define GROUPS_H
//Groups of people one of the base classes
class groups {
int num_of_people;
float avg_age;
friend class SoccerTeams;
public:
//virtual string getclass() { return char2str(typeid(*(this)).name()); }
groups(int numb = 0): num_of_people(numb) {};
~groups(){};
};
//SoccerTeam group class
class SoccerTeams : public groups {
std::string teamName;
std::vector<SoccerTeams> teams;
int teamId;
public:
Players player;
void addManager();
std::string nameTeam(int);
void deletePlayer(int);
void showTeam();
void addPlayer();
void showPlayers();
void showManagers();
void exportToFile(const char *);
SoccerTeams() {};
SoccerTeams(std::string, int);
~SoccerTeams() {};
};
//FanClub group class
class FanClubs : public groups{
std::string clubName;
int clubId;
std::vector<FanClubs> fanclubs;
public:
Fans fan;
void addFans();
void showFans();
FanClubs() {};
FanClubs(std::string, int);
~FanClubs() {};
};
#endif
groups.cpp
#include <algorithm>
#include <iostream>
#include <vector>
#include <typeinfo>
#include <boost/units/detail/utility.hpp>
#include <cstdlib>
#include <fstream>
#include <list>
#include "groups.h"
using namespace std;
//Fan Club member functions
FanClubs::FanClubs(string name, int id) {
clubName = name;
clubId = id;
fanclubs.push_back(*this);
};
void FanClubs::showFans() {
cout << "Players in " << fanclubs.begin() -> clubName << endl;
fan.showFanas();
}
void FanClubs::addFans() {
int choice = 0;
cout << "1. Add a bunch of fans\n2. Add custom fans\nChoice: ";
cin >> choice;
switch(choice) {
case 1: {
int requirement;
cout << "How many fans do you need: ";
cin >> requirement;
static const string names[] = {
"Margarita", "Amalia", "Sam", "Mertie", "Jamila", "Vilma",
"Mazie", "Margart", "Lindsay", "Kerstin", "Lula", "Corinna", "Jina",
"Jimmy", "Melynda", "Demetrius", "Beverly", "Olevia", "Jessika",
"Karina", "Abdallah", "Max", "Prateek", "Aghaid"
};
for (int i = 0; i < requirement; ++i) {
fan.name = names[rand() % 24];
fan.age = (rand() % 80 + 1);
fan.sex = ((rand() % 2) ? 'M' : 'F');
fan.under_auth = false;
fan.auth_level = 0;
fans.push_back(fan);
}
break;
}
case 2: {
int requirement;
cout << "How many fans you want to add?\nnumber: ";
cin >> requirement;
for (int i = 0; i < requirement; ++i) {
cout << "======Fan " << i + 1 << "=======\n";
cout << "Enter name: ";
cin >> fan.name;
cout << "Enter age: ";
cin >> fan.age;
cout << "Enter sex: ";
cin >> fan.sex;
fan.under_auth = false;
fan.auth_level = 0;
fans.push_back(fan);
}
break;
}
default:
cout << "Incorrect choice\n";
break;
}
}
//Soccer Teams member functions
string SoccerTeams::nameTeam(int id) {
return teams.begin() -> teamName;
}
void SoccerTeams::showPlayers() {
cout << "Players in " << teams.begin() -> teamName << endl;
player.showPlayas();
}
void SoccerTeams::showManagers() {
int counter = 1;
list<ManagingDirectors>::iterator i;
for (i = directors.begin(); i != directors.end(); i++) {
cout << "Director " << counter << endl;
cout << "Works for team " << nameTeam(i -> directorId) << endl;
cout << "Name: " << i -> name << endl;
cout << "Sex: " << i -> sex << endl;
counter++;
}
}
void SoccerTeams::addPlayer() {
int newId;
int number;
cout << "Number of players to be added: ";
cin >> number;
for (int i = 0; i < number; ++i) {
cout << "\nEnter player name: ";
cin >> player.name;
cout << "Enter sex(M/F): ";
cin >> player.sex;
cout << "Enter age: ";
cin >> player.age;
cout << "Enter player id(0 for random id): ";
cin >> newId;
newId == 0 ? player.playerId = (rand() % 100 + 1) : player.playerId = newId;
player.under_auth = true;
player.auth_level = 0;
players.push_back(player);
teams.begin()->num_of_people++;
}
}
void SoccerTeams::deletePlayer(int id) {
std::vector<Players>::iterator i;
for (i = players.begin(); i != players.end(); ) {
if(i->playerId == id) {
i = players.erase(i);
teams.begin()->num_of_people--;
}
else
i++;
}
}
void SoccerTeams::showTeam() {
vector<SoccerTeams>::iterator i;
for (i = teams.begin(); i != teams.end(); ++i) {
cout << "\nTeam name: " << i -> teamName << endl;
cout << "Team id: " << i -> teamId << endl;
cout << "Number of players: " << i -> num_of_people << endl;
cout << "Average age: " << i -> player.ageCalc()/teams.begin() -> num_of_people << endl;
}
}
SoccerTeams::SoccerTeams(string tn, int id) {
teamName = tn;
teamId = id;
teams.push_back(*this);
};
void SoccerTeams::addManager() {
ManagingDirectors mandir;
int number;
cout << "How many managers you want to add: ";
cin >> number;
for (int i = 0; i < number; i++) {
cout << "Manager " << i + 1 << endl;
cout << "Enter name of the director: ";
cin >> mandir.name;
cout << "Enter the age: ";
cin >> mandir.age;
cout << "Enter the sex(M/F): ";
cin >> mandir.sex;
mandir.directorId = teams.begin() -> teamId;
mandir.auth_level = 3;
mandir.under_auth = false;
directors.push_front(mandir);
}
}
void SoccerTeams::exportToFile(const char *filename) {
ofstream outfile;
outfile.open(filename, ios::out);
vector<Players>::iterator i;
int counter = 1;
outfile << "Team Data" << endl;
outfile << "Team name : " << teamName << "\nPlayers : " << teams.begin() -> num_of_people << endl;
outfile << "Average age: " << teams.begin() -> player.ageCalc()/teams.begin() -> num_of_people << endl;
for (i = players.begin(); i != players.end(); ++i) {
outfile << "\nPlayer " << counter << endl;
outfile << "Name: " << i -> name << endl;
outfile << "Sex : " << i -> sex << endl;
outfile << "Age : " << i -> age << endl;
outfile << "Pid : " << i -> playerId << endl;
counter++;
}
outfile.close();
}
people.h
#ifndef PEOPLE_H
#define PEOPLE_H
//People base class
class people {
string name;
char sex;
int age;
bool under_auth;
int auth_level;
friend class SoccerTeams;
friend class Players;
friend class Fans;
friend class FanClubs;
public:
//virtual string getclass() { return char2str(typeid(*(this)).name()); }
people(){};
~people(){};
//virtual int get_age(){ return this->age; };
};
//players class people
class Players : public people {
int playerId;
int avgAge;
friend class SoccerTeams;
public:
void showPlayas();
float ageCalc();
Players(){};
~Players(){};
};
std::vector<Players> players;
//Class Managing Directors people
class ManagingDirectors : public people {
int directorId;
friend class SoccerTeams;
public:
ManagingDirectors(int);
ManagingDirectors() {};
~ManagingDirectors(){};
};
std::list<ManagingDirectors> directors;
//Fans people class
class Fans : public people {
public:
void showFanas();
Fans(){};
~Fans(){};
};
std::vector<Fans> fans;
#endif
people.cpp
#include <algorithm>
#include <iostream>
#include <vector>
#include <typeinfo>
#include <boost/units/detail/utility.hpp>
#include <cstdlib>
#include <fstream>
#include <list>
#include "people.h"
using namespace std;
const int vector_resizer = 50;
string char2str(const char* str) { return boost::units::detail::demangle(str); }
//Fan class member functions
void Fans::showFanas() {
int counter = 1;
vector<Fans>::iterator i;
for (i = fans.begin(); i != fans.end(); ++i) {
cout << "\nFan " << counter << endl;
cout << "Name: " << i -> name << endl;
cout << "Sex: " << i -> sex << endl;
cout << "Age: " << i -> age << endl;
counter++;
}
}
//Players class member functions
float Players::ageCalc() {
int totalAge = 0;
vector<Players>::iterator i;
for (i = players.begin(); i != players.end(); ++i) {
totalAge += i->age;
}
return totalAge;
}
void Players::showPlayas() {
int counter = 1;
vector<Players>::iterator i;
for (i = players.begin(); i != players.end(); ++i) {
cout << "\nPlayer " << counter << endl;
cout << "Name: " << i -> name << endl;
cout << "Sex: " << i -> sex << endl;
cout << "Age: " << i -> age << endl;
cout << "Player id: " << i -> playerId << endl;
counter++;
}
}
//Member functions of Managing DIrectos
ManagingDirectors::ManagingDirectors(int number) {
directorId = number;
};
In addition to these files, I also have a makefile.
//makefile
footballmaker: main.o groups.o people.o
gcc -o main main.o groups.o people.o
rm groups.o people.o
Also here's all the code in one file, the way it works right now.
I'm getting the following error when I try to make the program,
gcc -o main main.o groups.o people.o
groups.o:(.bss+0x0): multiple definition of `players'
main.o:(.bss+0x0): first defined here
groups.o:(.bss+0x20): multiple definition of `directors[abi:cxx11]'
main.o:(.bss+0x20): first defined here
groups.o:(.bss+0x40): multiple definition of `fans'
main.o:(.bss+0x40): first defined here
people.o:(.bss+0x0): multiple definition of `players'
main.o:(.bss+0x0): first defined here
people.o:(.bss+0x20): multiple definition of `directors[abi:cxx11]'
main.o:(.bss+0x20): first defined here
people.o:(.bss+0x40): multiple definition of `fans'
main.o:(.bss+0x40): first defined here
...
collect2: error: ld returned 1 exit status
makefile:3: recipe for target 'footballmaker' failed
make: *** [footballmaker] Error 1
The entire error was over 400 lines long, it is attached here.
I'm not sure how I can include files, so that I don't duplicate them, since the files are needed to make the program work, would there be a better way to split my code into files?

Answer 1

You define (not just declare!) variables at file scope in header file people.h. Such a variable definition will be visible to all other translation units at time of linkage. If different translation units, e.g. people.cpp and main.cpp, now include people.h, then this is as if these variable definitions had been written directly into both people.cpp and main.cpp, each time defining a separate variable with the same name at a global scope.
To overcome this, declare the variables in the header file, but define it in only one translation unit, e.g. people.cpp. Just declaring a variable means putting keyword extern in front of it (telling the compiler that variable definition will be provided by a different translation unit at the time of linking):
// people.h
extern std::vector<Players> players;
extern std::list<ManagingDirectors> directors;
extern std::vector<Fans> fans;
// people.cpp
std::vector<Players> players;
std::list<ManagingDirectors> directors;
std::vector<Fans> fans;