Unordered map LNK2001

Question

I'm trying to put items in a 2dimensional unordered map like this:

#include <unordered_map>
#include <string>
#include <vector>

class Scene {
protected:
    static std::unordered_map<std::string, std::unordered_map<std::string, Mesh>> Meshes;

public:
    static void loadMesh(std::string filename) {
        std::string meshName;
        std::vector<GLfloat> v;
        std::vector<GLfloat> vn;
        etc..

        Meshes[filename].emplace(std::make_pair(meshName, Mesh(v, vn, vt, f)));  // This causes the error
    }
}

I've also tried using this:

Meshes[filename][meshName] = Mesh(v, vn, vt, f);

but it keeps giving me this very long error:

Error   2   error LNK2001: unresolved external symbol "protected: static class        std::unordered_map<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::unordered_map<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class Mesh,struct std::hash<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,struct std::equal_to<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,class std::allocator<struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const ,class Mesh> > >,struct std::hash<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,struct std::equal_to<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,class std::allocator<struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const ,class std::unordered_map<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class Mesh,struct std::hash<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,struct std::equal_to<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >,class std::allocator<struct std::pair<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const ,class Mesh> > > > > > Scene::Meshes" (?Meshes@Scene@@1V?$unordered_map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$unordered_map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@VMesh@@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@VMesh@@@std@@@2@@2@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$unordered_map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@VMesh@@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@VMesh@@@std@@@2@@2@@std@@@2@@std@@A)   C:\Users\Gebruiker\Documents\Visual Studio 2013\Projects\C++ Projects\Engine\Engine\Scene.obj

Am I using unordered maps the wrong way, or am I missing something?

You didn't _define_ that static member. See the duplicate question for details — Lightness Races in Orbit, Sep 28 '14 at 17:16
If you declare a static variable in a class like that, you need to define it once somewhere, usually in the corresponding .cpp file: `std::unordered_map<...> Scene::Meshes;` — user123, Sep 28 '14 at 17:16

score 2 · Accepted Answer · answered Sep 28 '14 at 17:17

2

You declared Meshes but you didn't define it. Add a line like this

std::unordered_map<std::string, std::unordered_map<std::string, Mesh>> Scene::Meshes;

to one (and only one) .cpp file.

answered Sep 28 '14 at 17:17

Adam

16,808
7
52
98

Unordered map LNK2001

1 Answers1