Linking namespace to executable

edit

Hello,

i have two executable i build them with:

 add_executable(MapProcessing src/MapProcessing.cpp BasicCalculation.cpp)

added minimal example

function header MapProcessing.h

#ifndef MAPPROCESSING_H_
#define MAPPROCESSING_H_

#include <BasicCalculation.h>

class MapProcessing
{
public:
    MapProcessing();
private:
    void DoSomething();
};

#endif /* MAPPROCESSING_H_ */

function cpp

#include "map_processing.h"

void MapProcessing::DoSomething(){
     Eigen::Vector2d vector(1,0);
    double test=BasicCalculation::test;
    int p=BasicCalculation::a();
    double test=BasicCalculation::AngleBetweenXaxisAndVector(vector);
  }
}

header namespace:

#ifndef BASICCALCULATION_H_
#define BASICCALCULATION_H_

#include <Eigen/Core>
#include <Eigen/Eigenvalues>
#include <Eigen/Geometry>

namespace BasicCalculation{
  double AngleBetweenXaxisAndVector(const Eigen::Vector2d& vector);
  static double test=2;
  static int a(){return 1;}
};

#endif /* BASICCALCULATION_H_ */

cpp namespace

#include "BasicCalculation.h"
using namespace BasicCalculation;

double AngleBetweenXaxisAndVector(const Eigen::Vector2d& vector)
{
   calculate angle;
   return angle;
}

when i build this. I get an error

undefined reference to `BasicCalculation::AngleBetweenXaxisAndVector(Eigen::Matrix<double, 2, 1, 0, 2, 1> const&)'

but variable test and function a() are working.

I have no idea why...

can u please help?