Defining global variables over multiple files outside main loop - c++

Question

I know it's not very good, but I need global variables across multiple files in my program. These are my graphics window's variables:
Name
Size
Status
.
I know I can make a .h file and declare all variables:
#pragma once
extern std::string GameName;
extern sf::RenderWindow Window;
extern std::string Status;
.
Then I want to define my variables in my main.cpp, so all files can access these values. But I cannot define these unless they are in the int main() loop. Is there another way, so I can define these variables not in main loop?
EDIT
Using Visual Studio 2017.
Errors:
LNK2001 unresolved external symbol "class sf::RenderWindow Window"
(?Window##3VRenderWindow#sf##A) Cubes
Library C:\Users\George\Documents\C++\Files\Libraries\Cubes
Library\Cubes Library\Cubes Library.obj 1
.
LNK2001 unresolved external symbol "class
std::basic_string,class
std::allocator > Status"
(?Status##3V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std##A) Cubes
Library C:\Users\George\Documents\C++\Files\Libraries\Cubes
Library\Cubes Library\Cubes Library.obj 1
.
LNK1120 2 unresolved externals Cubes
Library C:\Users\George\Documents\C++\Files\Libraries\Cubes
Library\Debug\Cubes Library.dll 1

Answer 1

You can declare them in your main.cpp file, but in order to make them globally accessible, you have to define them outside your main function/loop. If you decalre them inside your main function/loop, they are local variables and cannot (easily) be accessed globally. Doing it this way combined with the header file you suggested will work.
// Global variables...
std::string GameName;
sf::RenderWindow Window;
std::string Status;
int main()
{
return 0;
}
You could also put them in another file, for example globals.cpp.

Answer 2

You would do it like this...
File: Main.h
#ifndef __MAIN_H__
#define __MAIN_H__
#include <string>
extern std::string GameName;
//extern sf::RenderWindow Window;
extern std::string Status;
#endif
File: Main.cpp
#include "stdafx.h"
#include <iostream>
#include "Main.h"
std::string GameName;
//sf::RenderWindow Window;
std::string Status;
extern void foo(); // Function Prototype
int main()
{
GameName = "none";
Status = "none";
foo();
std::cout << GameName << " - " << Status << std::endl;
std::cout << "(HIT A KEY TO CONTINUE)" << std::endl;
getchar();
return 0;
}
File: Other.cpp
#include "stdafx.h"
#include "Main.h"
void foo()
{
// Global variables declared in Main.cpp are now accessible here
GameName = "Horizon New Dawn";
Status = "Finished";
}

Answer 3

This is how to do it using globals in a DLL.
// File: DLLGlobals.h
// This file is used in the DLL project
#ifndef __GLOBALS_H__
#define __GLOBALS_H__
#include <string>
extern "C"
{
extern __declspec(dllexport) std::string GameName;
extern __declspec(dllexport) std::string Status;
}
#endif//__GLOBALS_H__
// File: DLLGlobals.cpp
#include "stdafx.h"
#include "DLLGlobals.h"
extern "C"
{
// Define Global Variables (no C++ mangling)
__declspec(dllexport) std::string GameName = "Dishonored 2";
__declspec(dllexport) std::string Status = "Not Started";
}
// File: DLL.h
#ifndef __DLL_H__
#define __DLL_H__
// This file is included by code using the DLL project
#include <string>
extern "C"
{
__declspec(dllimport) std::string GameName;
__declspec(dllimport) std::string Status;
}
#endif//__DLL_H__
// File: Main.cpp
#include "stdafx.h"
#include <iostream>
#include "Main.h"
#include "<path_to_dll_header>\DLL.h"
int main()
{
std::cout << GameName << ": " << Status << std::endl;
std::cout << "(HIT A KEY TO CONTINUE)" << std::endl;
getchar();
return 0;
}