C++ 无序地图LNK2001

我试图将项目放入二维无序地图中，如下所示：

#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
    }
}

但它总是给我一个很长的错误：

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

Error 2 Error LNK2001:未解析的外部符号“protected:static class std:：unordered_map Scene:：mesh”(?Meshes@Scene@@1V？$无序_map@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@V？$无序_map@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@VMesh@@U$hash@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@@2@U？$equal_to@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@@2@V?$allocator@U？$p空气@$$CBV？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@VMesh@@@std@@@2@@2@U?$hash@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@@2@U？$equal_to@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@@2@V?$allocator@U？$pair@$$CBV？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@V？$无序_map@V？$bas集成电路_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@VMesh@@U$hash@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@@2@U？$equal_to@V？$basic_string@DU？$char_traits@D@性病病毒$allocator@D@2@@std@@@2@V?$allocator@U？$pair@$$CBV？$basic_string@DU？$char_traits@D@性病病毒$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

---

是我使用无序贴图的方式不对，还是我遗漏了什么？

您声明了

网格，但没有定义它。添加一行如下内容

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

std:：无序地图场景：：网格；

到一个（且仅一个）.cpp文件。
您没有定义该静态成员。有关详细信息，请参阅重复问题如果您在这样的类中声明一个静态变量，则需要在某个地方定义它一次，通常在相应的.cpp文件中：
std:：unordered\u map Scene:：mesh；
std::unordered_map<std::string, std::unordered_map<std::string, Mesh>> Scene::Meshes;