Question

I have a few static unordered_maps in my application that I would like to be able to initialize on start up. They are not part of a class. In my initial setup, the header and source file were as follows:

namespace Game
{
    namespace Elements
    {

        enum Element
        {
            Air = 1,
            Dark = 2,
            Earth = 4,
            Elementless = 8,
            Fire = 16,
            Ice = 32,
            Light = 64,
            SpaceTime = 128,
            Thunder = 256,
            Water = 512,
        };
        static boost::unordered_map<Element, std::string> ElementNameMap;
        static boost::unordered_map<std::string, Element> NameElementMap
        }
}

And the source file:

#include "Elements.h"

using namespace std;
using namespace Game::Elements;

boost::unordered_map<Element, std::string> ElementNameMap = boost::assign::map_list_of
    (Element::Air, string("Air"))
    (Element::Dark, string("Dark"))
    (Element::Earth, string("Earth"))
    (Element::Elementless, string("Elementless"))
    (Element::Fire, string("Fire"))
    (Element::Ice, string("Ice"))
    (Element::Light, string("Light"))
    (Element::SpaceTime, string("SpaceTime"))
    (Element::Thunder, string("Thunder"))
    (Element::Water, string("Water"))
    ;

boost::unordered_map<std::string, Element> NameElementMap = boost::assign::map_list_of
    (string("Air"), Element::Air)
    (string("Dark"), Element::Dark)
    (string("Earth"), Element::Earth)
    (string("Elementless"), Element::Elementless)
    (string("Fire"), Element::Fire)
    (string("Ice"), Element::Ice)
    (string("Light"), Element::Light)
    (string("SpaceTime"), Element::SpaceTime)
    (string("Thunder"), Element::Thunder)
    (string("Water"), Element::Water)
    ;

However, whenever I tried doing this then tried to do a lookup on the maps (i.e. Game::Elements::NameElementMap[std::string(“Air”)] ) it always returns an empty string, and the size in that use context is 0.

I tried moving the initialization into the header file (i.e. in the header file putting

static boost::unordered_map<Element, std::string> ElementNameMap = boost::assign::map_list_of
    (Element::Air, string("Air"))
    (Element::Dark, string("Dark"))
    (Element::Earth, string("Earth"))
    (Element::Elementless, string("Elementless"))
    (Element::Fire, string("Fire"))
    (Element::Ice, string("Ice"))
    (Element::Light, string("Light"))
    (Element::SpaceTime, string("SpaceTime"))
    (Element::Thunder, string("Thunder"))
    (Element::Water, string("Water"))
    ;
static boost::unordered_map<std::string, Element> NameElementMap = boost::assign::map_list_of
    (string("Air"), Element::Air)
    (string("Dark"), Element::Dark)
    (string("Earth"), Element::Earth)
    (string("Elementless"), Element::Elementless)
    (string("Fire"), Element::Fire)
    (string("Ice"), Element::Ice)
    (string("Light"), Element::Light)
    (string("SpaceTime"), Element::SpaceTime)
    (string("Thunder"), Element::Thunder)
    (string("Water"), Element::Water)
    ;

but the compiler then complained about having no default constructor. What am I doing wrong?

thanks in advance

Answer 1

You have to put the definitions in the correct namespace. Otherwise you are defining two new maps in the global namespace, instead of the ones in Game::Elements:

namespace Game {
namespace Elements {

boost::unordered_map<Element, std::string> ElementNameMap = boost::assign::map_list_of
    (Air, string("Air"))
    (Dark, string("Dark"))
...

}
}

(Also enums don’t create a new namespace, so it’s just Air, not Element::Air.)