Linking error when compiling code using cython

Question

I have the following c++ and header file, which I would like to compile in Cython: c++ code:

\\ CA.cpp c++ code

#include "CA.h"
#include<iostream>
#include <vector>
Cell::Cell() {}
// construct cell: cell is defined with position (x,y,z coordinates) and neighborhood
Cell::Cell(int x, int y, int z) {
    this->x = x;
    this->y = y;
    this->z = z;
    std::vector<int> ngh;
}

// Return the neighbors of the cell
void Cell::neighbors( ) {
    std::vector<int> a{ -1, 0, 1 };
    std::vector<int> ranges(gridSize, 0);
    for (int i = 0; i < ranges.size(); i++) {
        ranges[i] = i;
    }


    for (int i = -1; i <= 1; i++) {
        for (int j = -1; j <= 1; j++) {
            for (int k = -1; k <= 1; k++) {
                int x_ngh = ranges[Cell::x + i];
                int y_ngh = ranges[Cell::y + j];
                int z_ngh = ranges[Cell::z + k];

            int id_ngh = x_ngh + (y_ngh - 1) * gridSize + (z_ngh - 1) * gridSize * gridSize;
            Cell:ngh.push_back(id_ngh);
            }
        }
    }
}

and header file:

\\CA.h
    #ifndef CA_H
    #define CA_H
    #include <vector>

    const int gridSize = 400;
    class Cell {
    public:
        int x, y, z;
        std::vector<int> ngh;
        Cell();
        Cell(int x, int y, int z);
        void neighbors();
    };
    #endif

In order to compile the code using cython I created CA.pxd file:

cdef extern from "CA.cpp":
    pass

# Declare the class with cdef
cdef extern from "CA.h":
    cdef cppclass Cell:
        Cell() except +
        Cell(int, int, int) except +
        int x,y,z
        neighbors()

and CA.pyx

# distutils: language = c++
from CA cimport *
from libcpp.vector cimport vector
cdef class PyCell:
    cdef  Cell c_cell

    def __cinit__(self, int x, int y, int z):
        self.c_cell = Cell(x,y,z)

    def neighbors(self):
        return self.c_cell.neighbors()

Finally, I created setup.py file:

from Cython.Build import cythonize
setup(ext_modules=cythonize("CA.pyx"))

When I run the command: python setup.py build_ext --inplace

I get an error LINK : error LNK2001: unresolved external symbol PyInit_CA. I don't know why. Any help greatly appreciated.