Manipulating a global static variable

Question

Suppose I have main.cpp , file.h and file.cpp . Where file.cpp implements all the prototypes in file.h and main.cpp includes file.h .

Very simple structure. I was wondering If i declared a static global variable in main.cpp would it be possible to access to such variable when implementing all the functions in file.cpp ? With a quick attempt this doesn't seem to be case... I can't even compile it.

But would it be possible to work this around?

Just to clarify I have

file.h:

#ifndef __FILE_H
#define __FILE_H
#include <iostream>

void my_func();

#endif

file.cpp

#include "file.h"

using namespace std;

void my_func() {
    //do something with my_static_var
}

and main.cpp

#include "file.h"

static int my_var = 0;

int main(int argc, char** argv) {
    my_func();
    return 0;
}

Assume no classes involved

Answer 1

A variable with internal linkage can be referred to only from scopes within its translation unit (which typically means its source file). A variable declared with the static keyword has internal linkage.

A variable with external linkage can be referred to from other translation units (other source files). A variable has external linkage if it is not in an anonymous namespace and:

• it is declared with the extern keyword, or
• it is namescape-scope (such as my_var in the question) and is declared with neither const nor static (unlike my_var in the question).

Reference: storage duration

Answer 2

No. The static here literally means "don't let me do" what you're trying to do. It makes the object private to that translation unit, with internal linkage .

Remove the static and you'll be golden (use an extern declaration elsewhere to bring it into scope), though you should consider avoiding globals.