Error: invalid use of member in static member function

Question

I have two classes, and this is the header of one of them:

#ifndef WRAPPER_HPP
#define WRAPPER_HPP

#include 

using namespace std;

class W         


        

Answer 1

You are using a static variable

static SDL_Surface *screen;

in your code.

In C++ when you declare a static variable in the .h (or .hpp) you are creating a variable that is general (static) to the class. Thus, to use it in another file you have to redeclare it (which I'm guessing you didn't) to create a variable in that file referencing the static one. In your case put this:

SDL_Surface* Wrapper::screen;

in the .cpp file.

I'm not sure the theory is well explained, but it works like that.