LNK2019 Error on overloaded output operator - c++

Question

I'm getting the following error from this code:
Error 1 error LNK2019: unresolved external symbol "class std::basic_ostream > & __cdecl operator<<(class std::basic_ostream > &,class Point const &)" (??6#YAAAV?$basic_ostream#DU?$char_traits#D#std###std##AAV01#ABV?$Point#N###Z) referenced in function _main G:\C++ Part II\Final Exam\Point\Point\Source.obj Point
I know this error typically means that I don't have a function defined, however, it is defined. The program compiles if I comment out the cout statement in main. I'm guessing I'm missing something with my Template designation?
#include <iostream>
using namespace std;
template <class T>
class Point{
private:
T x, y;
public:
Point(): x(0), y(0) {cout << "Default Constructor\n";};
Point(T a, T b): x(a), y(b) {cout << "Parameterized Constructor\n";};
Point(const Point &rhs);
~Point() {cout << "Destructor\n";};
friend ostream &operator<<(ostream &os, const Point<T> &X);
};
int main(){
Point <double> B;
cout << B << endl;
return 0;
}
template <class T>
Point<T>::Point(const Point &rhs)
{
x = rhs.x;
y = rhs.y;
cout << "Copy Constructor\n";
}
template <class T>
ostream &operator<<(ostream &os, const Point<T> &X)
{
os << "(" << X.x << ", " << X.y << ")";
return os;
}

Answer 1

The function you have declared as friend in the class isn't actually the same as the one you implemented. It's a templated function and the declaration needs to reflect that:
template <class T> friend ostream &operator<<(ostream &os, const Point<T> &X);