LNK2001错误如何解决？

VS报错：

LNK2001 无法解析的外部符号 "private: static class D2Dcore * TinyAVG::pTinyAVG_D2Dcore" (?pTinyAVG_D2Dcore@TinyAVG@@0PAVD2Dcore@@A) TinyAVG F:\文档\TinyAVG\TinyAVG\TinyAVG\TinyAVG.obj 1

#pragma once
#include"tinyxml2.h"
#include"D2Dcore.h"

#define WINDOW_WIDTH 1440
#define WINDOW_HEIGHT 810

class TinyAVG
{
public:
    TinyAVG();
    ~TinyAVG();

    HRESULT Initialize(HINSTANCE hInstance);
    void RunMessageLoop();

    static LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam);
private:
    HWND m_hwnd;
    static D2Dcore TinyAVG_D2Dcore;
};

D2Dcore是自定义的类，声明放在了D2Dcore.h当中
为什么出现这种错误？

要实现比静态变量TinyAVG_D2Dcore，TinyAVG.cpp文件中增加
D2Dcore TinyAVG::TinyAVG_D2Dcore;