C++ Error : undefined reference to.. split()

#include "point.hpp"

//constructeur
point::point( std::string const& str )
{
...
}

void translate(int x, int y)
{
   this.coords[0]=this.coords[0]+x;
   this.coords[1]=this.coords[1]+y;
}
...

#ifndef POINT_HPP_INCLUDED
#define POINT_HPP_INCLUDED 

#include <string>
#include <vector>

class point
{
  public:

  // constructeur par defaut
  point() {}

 void display(std::ostream& os) const;
 void translate(int x, int y); //<=c'est cette fonction qui n'est pas reconnue comme membre

point.cpp: In function `void translate(int, int)':
point.cpp:122: error: invalid use of `this' in non-member function
point.cpp:123: error: invalid use of `this' in non-member function