C++ weird problem, Undefined reference
<p>getting error: neljastest.cpp: undefined reference to Vector2::Vector2(float, float)</p>

<p>neljastest.cpp:</p>

<pre><code>    #include &lt;cstdlib&gt;
#include &lt;iostream&gt;
#include "../include/Vector2.h"
#include "../include/neljas.h"

using namespace std;

int main (int argc, char* argv[]) {
     Vector2 p1 (1.0, 2.0);
     Vector2 p2 (0.0, 0.0);
     Vector2 p3 (5.0, 2.0);
    return EXIT_SUCCESS;
}
</code></pre>

<p>vector2.h:</p>

<pre><code>#ifndef VECTOR2_H
#define VECTOR2_H

#include &lt;iostream&gt;
using std::ostream;

class Vector2 {

public:
    float x;
    float y;

    Vector2();

    Vector2(float nx, float ny);

    float distanceFrom(Vector2 v);


};


ostream&amp; operator &lt;&lt; (ostream&amp; valja, Vector2 v);

#endif
</code></pre>

<p>vector2.cpp:</p>

<pre><code>    #include "../include/Vector2.h"
#include &lt;cmath&gt;

using namespace std;

Vector2::Vector2() {
    x = 0;
    y = 0;
}

Vector2::Vector2(float nx, float ny) {
    x = nx;
    y = ny;
}

float Vector2::distanceFrom(Vector2 v) {
    return sqrt( (x - v.x)*(x - v.x) + (y - v.y)*(y - v.y) );
}

ostream&amp; operator &lt;&lt; (ostream&amp; os, Vector2 v) {
    return os &lt;&lt; "(" &lt;&lt; v.x &lt;&lt; "," &lt;&lt; v.y &lt;&lt; ")";
}
</code></pre>
