C++ LNK 2001单例上未解析的外部符号

我正在用SFML和Box2D创建一个类似peggle的游戏，但是我的游戏singleton出现了这个错误

错误1错误LNK2001:未解析的外部符号“私有：静态类游戏*游戏：：s_pInstance”（？s_pInstance@Game@@0PAV1@A)C:\Users\UserName\Desktop\PeggleClone\Maze\Maze\Game.obj

Main.cpp

#include "Game.h"
#define SCALE 30.0f
#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600   

int _tmain(int argc, _TCHAR* argv[])
{
    Game* game = Game::GetInstance();

    game->Initialize(WINDOW_WIDTH, WINDOW_HEIGHT);

    //Stuff for timesteps
    float timenow = (float)GetTickCount();
    float timethen = (float)GetTickCount();
    float timeelapsed = 0.0f;


    while (true)
    {
        timeelapsed = (float)(timenow - timethen) / 1000.0f;

        if(game->Update(timeelapsed) < 0)
            break;
        game->Render();


        timethen = timenow;
        timenow = (float)GetTickCount();
    }

    game->Terminate();
    game->DeleteInstance();
    return 0;
}

---

修复了它，我需要通过在game.cpp顶部添加这一行来初始化游戏实例

Game* Game::s_pInstance = nullptr;

---

此外，如果您确实需要，我建议您使用。

#include "stdafx.h"
#include "Game.h"
#include "BaseGameState.h"
#include "MainMenuState.h"



bool Game::Initialize(unsigned int width, unsigned int height)
{
    // Set up render window
    gameWindow = new sf::RenderWindow(sf::VideoMode(width, height), "Peggle Ripoff");

    // Clear state machine
    m_vStates.clear();

    //Start on main menu
    PushState(MainMenuState::GetInstance());

    return true;
}

Game* Game::GetInstance( void )
{
    if( s_pInstance == nullptr )
        s_pInstance = new Game;

    return s_pInstance;
}

void Game::DeleteInstance( void )
{
    delete s_pInstance;
    s_pInstance = nullptr;
}

Game* Game::s_pInstance = nullptr;