How to declare a global variable that could be used in the entire program

Question

I have a variable that I would like to use in all my classes without needing to pass it to the class constructor every time I would like to use it. How would I accomplish th

Answer 1

global.h
extern int myVar;

global.cpp
#include "global.h"
int myVar = 0;  // initialize

class1.cpp
#include "global.h"
...

class2.cpp
#include "global.h"
...

class3.cpp
#include "global.h"
...

MyVar will be known and usable in every module as a global variable. You do not have to have global.cpp. You could initialize myVar in any of the class .cpp's but I think this is cleaner for larger programs.