Undefined reference to constructor and destructor c++

Question

The error that I'm getting is this:

||=== Build: Debug in Building Sim (compiler: GNU GCC Compiler) ===|
obj/Debug/main.o||In function `__static_initialization_and_destruction_0':|
/home/josh/Documents/cpp/building_sim/main.cpp|15|undefined reference to `User::~User()'|
/home/josh/Documents/cpp/building_sim/main.cpp|20|undefined reference to `User::~User()'|
/home/josh/Documents/cpp/building_sim/main.cpp|20|undefined reference to `Building::~Building()'|
/home/josh/Documents/cpp/building_sim/main.cpp|20|undefined reference to `User::~User()'|
||=== Build failed: 4 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

I've been having this error for a few days now and have seen a good 14-18 threads that have answers to this issue that do absolutely nothing for mine. At this point my project is made up of five files:

main.cpp
user.hpp
user.cpp
building.hpp
building.cpp

main.cpp links building.hpp and user.hpp, building and user.cpp link their respective header files and building.cpp links user.hpp.

I've tried building this project a multitude of times two different ways. I created a shell script to build all three cpp files to .o files and then join them (in all possible orders), and I tried simply g++ main.cpp building.cpp user.cpp in all possible orders and I created a Code::Blocks project to link all the files together manually. All of my header files have include guards, but I don't think that's an issue.

The full text of my files follows.

main.cpp

#include <stdio.h>
#include "building.hpp"
#include "user.hpp"

// TODO Text parsing
// TODO Resources
// TODO Generations

using namespace std;

//----------------------------------
//            Variables
//----------------------------------
//-----User------
User user(1000);

//---Buildings---
int numBuildings = 0;

Building building1(user, 10, 14, "George");
Building buildings[] = {building1};

int main(){

    return 0;
}

user.hpp

#include <stdio.h>

#ifndef user_h
#define user_h

class User{
public:
    User();
    ~User();

    User(int _money);

    int getMoney();
    void setMoney(int _money);

    int getBuildings();
    void setBuildings(int _buildings);

private:
    int money;
    int buildings;
};

#endif

user.cpp

#include "user.hpp"

User::User(){
    User::money = 1000;
    User::buildings = 0;
}

User::User(int _money){
    User::money = _money;
    setBuildings(getBuildings()+1);
}

int User::getMoney(){
    return User::money;
}

void User::setMoney(int _money){
    User::money = _money;
}

int User::getBuildings(){
    return User::buildings;
}

void User::setBuildings(int _buildings){
    User::buildings = _buildings;
}

building.hpp

#include <iostream>
#include <string>
#include "user.hpp"

#ifndef building_h
#define building_h

class Building{
public:
    Building();
    ~Building();

    Building(User user);
    Building(User user, int _cost, int _payout);
    Building(User user, int _cost, int _payout, std::string _name);

    int getCost();
    int getPayout();

private:
    int cost;
    int payout;
    std::string name;
};

#endif

building.cpp

#include "building.hpp"

Building::Building(){
    std::cout << "\n[ERROR] Default constructor used, no building created.\n";
}

Building::Building(User user){
    Building::cost = 10;
    Building::payout = 20;
    Building::name = "Generic";
    user.setBuildings(user.getBuildings()+1);
}

Building::Building(User user, int _cost, int _payout){
    Building::cost = _cost;
    Building::payout = _payout;
    Building::name = "Generic";
    user.setBuildings(user.getBuildings()+1);
}

Building::Building(User user, int _cost, int _payout, std::string _name){
    Building::cost = _cost;
    Building::payout = _payout;
    Building::name = _name;
    user.setBuildings(user.getBuildings()+1);
}

int Building::getCost(){
    return Building::cost;
}

int Building::getPayout(){
    return Building::payout;
}

Answer 1

You simply forgot to define the both destructors: User and Building in corresponding cpp modules.