Undefined reference, using SFML - c++

Question

I have begun learning SFML at the same time as C++ and do not understand the rules of using & and * in RenderWindow case. Could you help me?
Main class:
#include <SFML/Graphics.hpp>
#include "Square.h"
int main()
{
sf::RenderWindow window(sf::VideoMode(200, 200), "SFML works!");
Square sq(5,5);
while (window.isOpen())
{
sf::Event event;
while (window.pollEvent(event))
{
if (event.type == sf::Event::Closed)
window.close();
}
window.clear();
sq.draw(&window);
window.display();
}
return 0;
}
Square header:
#ifndef SQUARE_H
#define SQUARE_H
class Square
{
private:
sf::RenderWindow* window;
sf::RectangleShape rectangle;
int y;
int x;
public:
Square(int coordX, int coordY);
Square();
void draw(const sf::RenderWindow* target);
};
#endif
Square class:
#include <SFML/Graphics.hpp>
class Square{
sf::RectangleShape rectangle;
int y;
int x;
public:
Square(int coordX, int coordY)
: rectangle(), y(coordY),x(coordX)
{
rectangle.setSize(sf::Vector2f(10,100));
rectangle.setOrigin(5,50);
}
Square()
: rectangle(), y(5),x(5)
{
rectangle.setSize(sf::Vector2f(10,100));
rectangle.setOrigin(5,50);
}
void draw(sf::RenderWindow* target)
{
target->draw(rectangle);
}
I can't draw a square on RenderWindow:
main.cpp:(.text+0x17d): undefined reference to `Square::Square(int, int)'
main.cpp:(.text+0x211): undefined reference to `Square::draw(sf::RenderWindow const*)'
How can I make this work?

Answer 1

In C++, you have function declaration and function definition:
// declaration, typically in X.h
#pragma once // don't include this twice, my dear compiler
class X {
public:
void foo();
};
Implementation:
// X.cpp
#include "X.h"
void X::foo() { ...code .... }
// here you wrote
// class X { void foo(){} };
// which is a _declaration_ of class X
// with an _inline definition_ of foo.
Usage:
// main.cpp
#include "X.h"
Applying this pattern to your code should ensure that
every symbol is defined
no symbol is defined more than once

Answer 2

Remove square.cpp and change your square.h file to the following. Make sure you take back-up before changing your files.
#ifndef SQUARE_H
#define SQUARE_H
class Square
{
private:
sf::RenderWindow* window;
sf::RectangleShape rectangle;
int y;
int x;
public:
Square(int coordX, int coordY)
: rectangle(), y(coordY),x(coordX)
{
rectangle.setSize(sf::Vector2f(10,100));
rectangle.setOrigin(5,50);
}
Square()
: rectangle(), y(5),x(5)
{
rectangle.setSize(sf::Vector2f(10,100));
rectangle.setOrigin(5,50);
}
void draw(sf::RenderWindow* target)
{
target->draw(rectangle);
}
};
#endif