Problems on creating a static map as a class member [duplicate]

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• Initializing private static members 11 answers

At the moment I'm programming a 2D game framework with SDL and I have a problem with my sprite handler. I need a static map for my loaded textures.

SpriteHandler.cpp:

#include "SpriteHandler.h"


SpriteHandler::SpriteHandler(SDL_Renderer* rendere)
{
    renderer = rendere;
    console = new ConsoleHandler("SpriteHandler");
    console->printInfo("Initialisation ..");
}

bool SpriteHandler::RegisterTexture(int uuid, std::string file){
    std::string path = "./assets/textures/" + file;
    if (textures.count(uuid)){
        console->printWarning("UUID " + std::to_string(uuid) + " already registered! Skipping ..");
        return false;
    }
    if (!FileExists(path)){
        console->printWarning("Texture '" + file + "' cannot be found. Skipping ..");
        return false;
    }

    SDL_Texture* sprite = SDL_CreateTextureFromSurface(renderer, IMG_Load(path.c_str()));
    textures[uuid] = sprite;

    console->printInfo("Loaded " + file);

    return true;
}

bool SpriteHandler::FileExists(std::string StrFilename){
    GetFileAttributes(StrFilename.c_str());
    if (0xffffffff == GetFileAttributes(StrFilename.c_str()))
        return false;
    return true;
}

SpriteHandler::~SpriteHandler()
{
}

SpriteHandler.h:

#include <map>
#include <SDL.h>
#include <SDL_image.h>
#include <string>
#include <Windows.h>

#include "ConsoleHandler.h"

#pragma once
class SpriteHandler
{
private:
    static std::map<int, SDL_Texture*> textures; //Here the error occurs

    ConsoleHandler* console;
    SDL_Renderer* renderer;

    bool FileExists(std::string StrFilename);
public:
    SpriteHandler(SDL_Renderer* rendere);
    bool RegisterTexture(int uuid, std::string file);
    ~SpriteHandler();
};

Nothing special but I get a compiler error when I try to compile:

SpriteHandler.obj : error LNK2001: unresolved external symbol "private: static class std::map<int,struct SDL_Texture *,struct std::less<int>,class std::allocator<struct std::pair<int const ,struct SDL_Texture *> > > SpriteHandler::textures" (?textures@SpriteHandler@@0V?$map@HPAUSDL_Texture@@U?$less@H@std@@V?$allocator@U?$pair@$$CBHPAUSDL_Texture@@@std@@@3@@std@@A)

BTW: Sorry for bad English.