Singleton Implemenatatio链接器错误

Question

class Game
{
public:
    //! Returns the only instance of the game object
    static shared_ptr<Game> GetGameInstance();
    //! Function with continous loop for game play
    void GamePlay();
    //! The hidden constructor
    ~Game();

private:
    //! The hidden constructor
    Game();
    static shared_ptr<Game> _game;
};



//.cpp file

#include "Game.h"

shared_ptr<Game> Game::_game;

shared_ptr<Game> Game::GetGameInstance()
{
    if(_game == NULL)
    {
        _game.reset(new Game);
    }
    return _game;
}

void Game::GamePlay()
{
    shared_ptr<Graphics> myGameGraphics;

    while(!myGameGraphics->UserForcedExit())
    {
        myGameGraphics->drawMaze();
    }

}

Game::~Game()
{

}

我有上面的代码，但编译给我一个链接器错误：

Game.obj：错误LNK2019：未解析的外部符号“private：__thiscall Game :: Game（void）”（?? 0Game @@ AAE @XZ）在函数“public：static class boost :: shared_ptr __cdecl Game： ：GetGameInstance（void）“（？GetGameInstance @ Game @@ SA？AV？$ shared_ptr @ VGame @@@ boost @@ XZ）

任何人都可以帮忙......

Answer 1

试试这个：

shared_ptr<Game> Game::GetGameInstance()
{
    if(_game = NULL)
        _game = shared_ptr<Game>(new Game);

    return _game;
}