How to fix the FLTK header files from 'Programmin principles and practice Using C++' book?

Question

I Am following the "Programming principles and practice using C++" and got to chapter 12 where GUI gets introduced. However I can't get the custom header files from the book to work. After trying several guides of installing fltk specifically for this book I got the furthest with this guide: https://bumpyroadtocode.com/2017/08/05/how-to-install-and-use-fltk-1-3-4-in-visual-studio-2017-complete-guide/#comments

I made the same changes to the header files as they did which got rid of most of the errors but not all of them. After commenting out some duplicate declarations in the Simple_window.h and Simple_window.cpp I only got 7 errors left. But since I am new to C++ (Otherwise I probably wouldn't be reading this book) I can't get rid of the last few errors :(

These are the errors:

Severity    Code    Description Project File    Line    Suppression State
Error   LNK2005 "void __cdecl seed_randint(int)" (?seed_randint@@YAXH@Z) already defined in Graph.obj   Programming Principles and Practice Using C++   C:\Users\CM Storm i7\source\repos\Programming Principles and Practice Using C++\Programming Principles and Practice Using C++\Window.obj    1   
Error   LNK2005 "class std::mersenne_twister_engine<unsigned int,32,624,397,31,2567483615,11,4294967295,7,2636928640,15,4022730752,18,1812433253> & __cdecl get_rand(void)" (?get_rand@@YAAAV?$mersenne_twister_engine@I$0CA@$0CHA@$0BIN@$0BP@$0JJAILANP@$0L@$0PPPPPPPP@$06$0JNCMFGIA@$0P@$0OPMGAAAA@$0BC@$0GMAHIJGF@@std@@XZ) already defined in Graph.obj Programming Principles and Practice Using C++   C:\Users\CM Storm i7\source\repos\Programming Principles and Practice Using C++\Programming Principles and Practice Using C++\GUI.obj   1   
Error   LNK2005 "class std::mersenne_twister_engine<unsigned int,32,624,397,31,2567483615,11,4294967295,7,2636928640,15,4022730752,18,1812433253> & __cdecl get_rand(void)" (?get_rand@@YAAAV?$mersenne_twister_engine@I$0CA@$0CHA@$0BIN@$0BP@$0JJAILANP@$0L@$0PPPPPPPP@$06$0JNCMFGIA@$0P@$0OPMGAAAA@$0BC@$0GMAHIJGF@@std@@XZ) already defined in Graph.obj Programming Principles and Practice Using C++   C:\Users\CM Storm i7\source\repos\Programming Principles and Practice Using C++\Programming Principles and Practice Using C++\Simple_window.obj 1   
Error   LNK2005 "class std::mersenne_twister_engine<unsigned int,32,624,397,31,2567483615,11,4294967295,7,2636928640,15,4022730752,18,1812433253> & __cdecl get_rand(void)" (?get_rand@@YAAAV?$mersenne_twister_engine@I$0CA@$0CHA@$0BIN@$0BP@$0JJAILANP@$0L@$0PPPPPPPP@$06$0JNCMFGIA@$0P@$0OPMGAAAA@$0BC@$0GMAHIJGF@@std@@XZ) already defined in Graph.obj Programming Principles and Practice Using C++   C:\Users\CM Storm i7\source\repos\Programming Principles and Practice Using C++\Programming Principles and Practice Using C++\Window.obj    1   
Error   LNK2005 "void __cdecl seed_randint(int)" (?seed_randint@@YAXH@Z) already defined in Graph.obj   Programming Principles and Practice Using C++   C:\Users\CM Storm i7\source\repos\Programming Principles and Practice Using C++\Programming Principles and Practice Using C++\GUI.obj   1   
Error   LNK2005 "void __cdecl seed_randint(int)" (?seed_randint@@YAXH@Z) already defined in Graph.obj   Programming Principles and Practice Using C++   C:\Users\CM Storm i7\source\repos\Programming Principles and Practice Using C++\Programming Principles and Practice Using C++\Simple_window.obj 1   
Error   LNK1169 one or more multiply defined symbols found  Programming Principles and Practice Using C++   C:\Users\CM Storm i7\source\repos\Programming Principles and Practice Using C++\Debug\Programming Principles and Practice Using C++.exe 1   

This is Simple_window.h:

#include "GUI.h"    // for Simple_window only (doesn't really belong in Window.h)

using namespace Graph_lib;

// Simple_window is basic scaffolding for ultra-simple interaction with graphics
// it provides one window with one "next" button for ultra-simple animation

struct Simple_window : Graph_lib::Window {
    Simple_window(Point xy, int w, int h, const string& title);

    /*
        : Window(xy, w, h, title),
        button_pushed(false),
        next_button(Point(x_max() - 70, 0), 70, 20, "Next", cb_next) {
        attach(next_button);
    }
    */
    bool wait_for_button();
        // modified event loop
        // handle all events (as per default), but quit when button_pushed becomes true
        // this allows graphics without control inversion
    /*
    {
        while (!button_pushed) Fl::wait();
        button_pushed = false;
        Fl::redraw();
    }
    */
    Button next_button;
private:
    bool button_pushed;

    static void cb_next(Address, Address addr); // callback for next_button
    //  { reference_to<Simple_window>(addr).next(); }
    /*
    {
        static_cast<Simple_window*>(addr)->next();
    }
    */
    void next(); //{ button_pushed = true; }

};

And Finally this is Simple_window.cpp:

//
// This is a GUI support code to the chapters 12-16 of the book
// "Programming -- Principles and Practice Using C++" by Bjarne Stroustrup
//

#include "Simple_window.h"

//------------------------------------------------------------------------------

Simple_window::Simple_window(Point xy, int w, int h, const string& title) :
    Window(xy, w, h, title),
    next_button(Point(x_max() - 70, 0), 70, 20, "Next", cb_next),
    button_pushed(false)
{
    attach(next_button);
}

//------------------------------------------------------------------------------

bool Simple_window::wait_for_button()
// modified event loop:
// handle all events (as per default), quit when button_pushed becomes true
// this allows graphics without control inversion
{
    show();
    button_pushed = false;
#if 1
    // Simpler handler
    while (!button_pushed) Fl::wait();
    Fl::redraw();
#else
    // To handle the case where the user presses the X button in the window frame
    // to kill the application, change the condition to 0 to enable this branch.
    Fl::run();
#endif
    return button_pushed;
}

//------------------------------------------------------------------------------

void Simple_window::cb_next(Address, Address pw)
// call Simple_window::next() for the window located at pw
{
    reference_to<Simple_window>(pw).next();
}

//------------------------------------------------------------------------------

void Simple_window::next()
{
    button_pushed = true;
    hide();
}

//------------------------------------------------------------------------------

Answer 1

there are two options to solve this problem, though don't know, which is generaly better:

1) comment out random number generators in "std_lib_facilities.h" lines 218-228

or

2) Project - Properities - Linker - All options - Additional options => edit and add /FORCE:MULTIPLE

Both works for me, hope for you as well.