How to access members of the namespace in different files?

Amswer:

With help of an extern keyword, we can do this, see the below example code.

//common.h
#ifndef COMMON_H_INCLUDED
#define COMMON_H_INCLUDED
namespace ATIC
{
  extern int data;
}
#endif // COMMON_H_INCLUDED

//test.cpp
#include "common.h"
namespace ATIC
{
  int data = 27;
}

//main.cpp
#include <iostream>
#include "common.h"
int main()
{
    std::cout << ATIC::data << std::endl;
    return 0;
}