"Undefined symbols for architecture x86_64:" C++

Question

I've been going through StackOverflow, and it seems that although many others have had a similar issue to mine, I can't seem to work out what my problem is.

This is my first time working with c++. The assignment is to make a simple vector class, separated across 3 files. It also must be packaged in a namespace.

My issue is that when I run g++ -o test e_main.cpp in Terminal, I get the error:

Undefined symbols for architecture x86_64:
  "e_vector::MyVector::add(e_vector::MyVector)", referenced from:
      _main in e_main-eb4076.o
  "e_vector::MyVector::norm()", referenced from:
      _main in e_main-eb4076.o
  "e_vector::MyVector::print()", referenced from:
      _main in e_main-eb4076.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Here is my "e_vector.h" file:

namespace e_vector { 
  class MyVector {
  public:
    double x; // The X-component of vector
    double y; // The Y-component of vector
    double z; // The Z-component of vector
    double norm(); 
    void print(); 
    MyVector add(MyVector u); 
  };
}

Here is my 'functions.cpp' file:

#include <iostream>
#include <cmath>
#include <string>
#include "e_vector.h"
using namespace std;
using namespace e_vector;

double e_vector::MyVector::norm() {
    return (sqrt(x * x * y * y * z * z));
}

void e_vector::MyVector::print() {
    cout << "(" << x << "," << y << "," << z << ")";
}

MyVector e_vector::MyVector::add(MyVector u) {
    MyVector w; 
    w.x = x + u.x; 
    w.y = y + u.y;
    w.z = z + u.z;
    return w;
}

Finally, here is my "e_main.cpp":

#include <iostream>
#include <cmath>
#include <string>
#include "e_vector.h"
using namespace std;
using namespace e_vector;

int main() {
    MyVector v1 = {1.0, 1.0, 1.0}; 
    MyVector v2 = {1.0, 0.0, 0.0};
    MyVector v3;

    cout << " norm of v1 = " << v1.norm(); // Test norm method
    cout << " v1 = " ; 
    v1.print() ; // Test print method

    cout << " v2 = " ; 
    v2.print() ;

    v3 = v1.add(v2) ; // Test the add method
    cout << " v3 = "; 
    v3.print();

    return 0;
}

Am I perhaps linking the files together incorrectly? Thank you in advance and sorry if this is blatantly obvious!