Defining global constant in C++

Question

I want to define a constant in C++ to be visible in several source files. I can imagine the following ways to define it in a header file:

1. #define GLOBAL_

Answer 1

Definitely go with option 5 - it's type safe and allows compiler to optimize (don't take address of that variable :) Also if it's in a header - stick it into a namespace to avoid polluting the global scope:

// header.hpp
namespace constants
{
    const int GLOBAL_CONST_VAR = 0xFF;
    // ... other related constants

} // namespace constants

// source.cpp - use it
#include 
int value = constants::GLOBAL_CONST_VAR;