C++ 未定义的引用

链接器错误：

$ make
g++ -Wall -g main.cpp SDL_Helpers.cpp Game.cpp DrawableObject.cpp `sdl-config --cflags --libs` -lSDL_mixer
/tmp/ccdxzrej.o: In function `Game':
/home/brett/Desktop/SDL/Game.cpp:16: undefined reference to `Player::Player(Game*)'
/home/brett/Desktop/SDL/Game.cpp:16: undefined reference to `Player::Player(Game*)'
collect2: ld returned 1 exit status
make: *** [all] Error 1

main.cpp：

#include "Game.h"

int main()
{
    Game g;
    return 0;
}

游戏h：

#ifndef BRETT_GAME_H
#define BRETT_GAME_H

#include <cmath>
#include "SDL.h"
#include "SDL_Helpers.h"
#include <vector>

class DrawableObject;

class Game
{
public:
    SDL_Surface * screen;
    std::vector<DrawableObject*> sprites;

    Game();
};

#endif

DrawableObject.cpp：

#include "DrawableObject.h"
#include "Game.h"

DrawableObject::DrawableObject(Game * const game_)
    :   game(game_)
{

}

Player.h：

#ifndef PLAYER_H
#define PLAYER_H

#include <cmath>
#include "DrawableObject.h"

class Player : public DrawableObject
{
public:
    Player(Game * const game);

    void update(SDL_Event *event);
};

#endif

---

编译行中缺少Player.cpp。你有一个链接错误

编译行中缺少Player.cpp。你有一个链接错误

这不是一个循环依赖性问题（至少不像您目前提出的问题那样）。您忘记编译

Player.cpp

不是一个循环依赖性问题（至少，不是您当前提出的问题）。您忘了编译

Player.cpp

也许应该重命名该主题？这与循环依赖关系毫无关系。也许应该重命名主题？这与循环依赖关系无关。值得注意的是，循环依赖关系没有问题。忘记将其添加到我的makefile中了。谢谢。值得注意的是，循环依赖项没有问题。忘记将其添加到我的makefile中了。谢谢

#include "DrawableObject.h"
#include "Game.h"

DrawableObject::DrawableObject(Game * const game_)
    :   game(game_)
{

}

#ifndef PLAYER_H
#define PLAYER_H

#include <cmath>
#include "DrawableObject.h"

class Player : public DrawableObject
{
public:
    Player(Game * const game);

    void update(SDL_Event *event);
};

#endif

#include "Player.h"
#include "Game.h"

Player::Player(Game * const game)
    : DrawableObject(game)
{

}

void Player::update(SDL_Event *event)
{
    draw_circle(game->screen, 100, 100, 50, 0xff000000);
}