C++ "unresolved external symbol" using namespace from different project - c++

Question

I have two projects (call them Test and Intrados). Inside Intrados, I have the following namespace:
#include "Mapper.h"
#include "Director.h"
#include "Driver.h"
#include <iostream>
#include <string>
using namespace std;
namespace IntradosMediator {
void addVehicle(string);
}
void IntradosMediator::addVehicle(string vehicleName) {
Mapper* mapper = Mapper::getInstance();
mapper->addVehicle(vehicleName);
}
From within the Intrados project, calling "IntradosMediator::Mapper(addVehicle)" works just fine; yet, in project Test, the following code produces a link error:
#include "IntradosMediator.cpp"
#include "Mapper.h"
using namespace IntradosMediator;
int main(){
IntradosMediator::addVehicle("Car X");
return 0;
}
The error is:
Test.obj : error LNK2019: unresolved external symbol "public: static class Mapper *
__cdecl Mapper::getInstance(void)" (?getInstance#Mapper##SAPAV1#XZ) referenced in
function "void __cdecl IntradosMediator::addVehicle(class std::basic_string<char,struct
std::char_traits<char>,class std::allocator<char> >)"
(?addVehicle#IntradosMediator##YAXV?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##
std###Z)
I've made sure to add Intrados as a reference for Test, and also included it in the Include Directories. Not sure what to do here, since I'm new to C++. Thanks in advance for any advice.
Edit:
I'm adding the Mapper code here:
//.h
#ifndef MAPPER_H
#define MAPPER_H
#include <string>
using std::string;
class Mapper {
public:
static Mapper* getInstance();
void addVehicle(string);
private:
//this is a singleton
Mapper(){};
};
#endif
//.cpp
#include "Mapper.h"
#include <vector>
#include <iostream>
#include <string>
using namespace std;
vector<string> vehicleList;
Mapper* Mapper::getInstance(){
static Mapper instance;
return &instance;
}
void
Mapper::addVehicle(string vehicleName) {
vehicleList.push_back(vehicleName);
}

Answer 1

The error says the linker can't find Mapper::getInstance (it seems to find your addVehicle function just fine). Might you be failing to include the library that implements "Mapper" in your link?

Answer 2

Could you paste your code for class Mapper?
It seems like you are missing addVehicle function in that class, which is what the compiler is complaining about.