C++ Class expression parameter incorrect definition

Question

I'm learning C++ and currently experiencing weird problem with Class template. This is my header file:

#ifndef VECTOR_H
#define VECTOR_H
#include <iostream>
#include <list>

using namespace std;

template <int n>
class Vector {

public:
    list<float> coords;
    Vector();
    Vector(list<float> ncoords);
};

template <int n>
Vector<n>::Vector() {
    coords.assign(n, 0.0);
}
#endif

And this is my .cpp file:

#include "vector.h"
#include <list>

using std::ostream;
using namespace std;

template <int n>
Vector<n>::Vector(list<float> ncoords): coords {ncoords}{}

Everything works fine if I do Vector<2> vector;

But linker gives an error if I try to Vector<20> vector2 { list<float>{} };

Error message

undefined reference to `Vector<20>::Vector(std::list >)'

The question is - how can I solve this problem?

You can't implement templates in .cpp-Files, you have to put that in the header. — ipc, Mar 17 '13 at 20:11
Templates have to be implemented in headers. See [why](http://stackoverflow.com/questions/495021/why-can-templates-only-be-implemented-in-the-header-file). — Synxis, Mar 17 '13 at 20:15

score 2 · Accepted Answer · edited May 23 '17 at 11:50

2

Templates have to be implemented inside header files. This is due to the way linking works. Read the exhaustive answer here carefully. And the next time search before asking.

edited May 23 '17 at 11:50

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answered Mar 17 '13 at 20:15

Alexander Shukaev

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C++ Class expression parameter incorrect definition

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