Linker Command Failed

Question

Linker Command Failed

Estoy intentando recrear el clásico juego de cartas Siete y medio. Mi problema viene cuando al compilar lo que tengo escrito hasta ahora, XCode me da el siguiente error:

linker command failed with exit code 1 (use -v to see invocation)

Si doy click derecho y pulso "Reveal in log" lo que aparece es esto:

Undefined symbols for architecture x86_64:
  "modeA(std::__1::basic_ifstream<char, 
std::__1::char_traits<char> >&, int)", referenced from:
  _main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Aquí incluyo el código completo. Gracias :)

#include <iostream>
#include <string>
#include <fstream>
using namespace std;

float modeA(ifstream &file, int numCards);

int main(){
    srand(time(NULL));
    ifstream file;
    string fileName;
    int numCards;
    float sum;

    cin >> fileName;
    file.open(fileName);
    numCards = 3 + rand() % (5 - 3 + 1);
    sum = modeA(file, numCards);
    cout << sum;
    file.close();
    return 0;
}

float modeA(ifstream file, int numCards){
    int c = 0, card;
    float sum, cardValue;

    while (c == numCards){
        file >> card;
        if (card == 10){
            cardValue = 0.5;
        }
        else if (card == 11){
            cardValue = 0.5;
        }
        else if (card == 12){
            cardValue = 0.5;
        }
        else {
            cardValue = card;
        }
        sum += cardValue;
        cout << card << endl;
        c++;
    }

return sum;
}