实体组件系统未定义的符号

我是 c++ 的新手，我试图用 sfml 创建一个游戏，在这个游戏中，我正在尝试使用一个实体组件系统，我可以用它来做这个游戏和更远的游戏，但是当我编译时，我收到一个错误，我不知道如何解决它。

这是我的实体.hpp类：

#ifndef Entity_hpp
#define Entity_hpp
#include <stdio.h>
#include <iostream>
#include <vector>
#include <Component.hpp>
using namespace std;
class Entity {
private:
    vector<unique_ptr<Component>> _components;
public:
    void Start();
    void Update();
    void Draw();
    template <typename T, typename... TArgs> T& AddComponent(TArgs... args);
    template <typename T> T& GetComponent();
};
#endif /* Entity_hpp */

接下来是实体.cpp类：

#include "Entity.hpp"
void Entity::Update() {
    for (auto& c : _components) {
        c->Update();
    }
}
void Entity::Draw() {
    for (auto& c : _components) {
        c->Draw();
    }
}
void Entity::Start() {
    for(auto& c : _components) {
        c->Start();
    }
}
template <typename T, typename... TArgs>
T& Entity::AddComponent(TArgs... args) {
    T* component(new T(forward<T>(args)...));
    component->entity = this;
    unique_ptr<T> ptr{component};
    _components.emplace_back(move(ptr));
    return *component;
}
template <typename T> T& Entity::GetComponent() {
    T* c;
    if(find(_components.begin(), _components.end(), c) != _components.end()) {
        return &c;
    }
    return nullptr;
}

我添加组件的游戏类：

#include "Game.hpp"
void Game::Start() {
    auto& entity(_system.AddEntity());
    auto& m(entity.AddComponent<Movement>());
}
void Game::Update() {
}

最后是我的组件及其父组件：

#ifndef MovementComponent_hpp
#define MovementComponent_hpp
#include <stdio.h>
#include <Component.hpp>
class Movement : Component {
public:
    Movement() {};
    void Start() override {};
    void Update() override {};
    void Draw() override {};
};
#endif /* MovementComponent_hpp */

两者都在 cpp 文件中没有实现

#ifndef Component_hpp
#define Component_hpp
#include <stdio.h>
using namespace std;
class Entity;
class Component {
public:
    Entity* entity{nullptr};
    virtual void Start();
    virtual void Update();
    virtual void Draw();
    virtual ~Component();
};

#endif /* Component_hpp */

这是我得到的错误：

Ld /Users/joeywelvaadt/Library/Developer/Xcode/DerivedData/SFML-eeksqjpmpgsdomeiuuzvucxhodww/Build/Products/Debug/SFML.app/Contents/MacOS/SFML normal x86_64
    cd /Users/joeywelvaadt/Desktop/XCode/C++/SFML
    export MACOSX_DEPLOYMENT_TARGET=10.7
    /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -L/Users/joeywelvaadt/Library/Developer/Xcode/DerivedData/SFML-eeksqjpmpgsdomeiuuzvucxhodww/Build/Products/Debug -L/usr/local/lib -F/Users/joeywelvaadt/Library/Developer/Xcode/DerivedData/SFML-eeksqjpmpgsdomeiuuzvucxhodww/Build/Products/Debug -F/Library/Frameworks -filelist /Users/joeywelvaadt/Library/Developer/Xcode/DerivedData/SFML-eeksqjpmpgsdomeiuuzvucxhodww/Build/Intermediates/SFML.build/Debug/SFML.build/Objects-normal/x86_64/SFML.LinkFileList -Xlinker -rpath -Xlinker @loader_path/../Frameworks -mmacosx-version-min=10.7 -Xlinker -object_path_lto -Xlinker /Users/joeywelvaadt/Library/Developer/Xcode/DerivedData/SFML-eeksqjpmpgsdomeiuuzvucxhodww/Build/Intermediates/SFML.build/Debug/SFML.build/Objects-normal/x86_64/SFML_lto.o -stdlib=libc++ -fobjc-link-runtime -framework sfml-system -framework sfml-window -framework sfml-graphics -framework sfml-audio -framework sfml-network -Xlinker -dependency_info -Xlinker /Users/joeywelvaadt/Library/Developer/Xcode/DerivedData/SFML-eeksqjpmpgsdomeiuuzvucxhodww/Build/Intermediates/SFML.build/Debug/SFML.build/Objects-normal/x86_64/SFML_dependency_info.dat -o /Users/joeywelvaadt/Library/Developer/Xcode/DerivedData/SFML-eeksqjpmpgsdomeiuuzvucxhodww/Build/Products/Debug/SFML.app/Contents/MacOS/SFML
Undefined symbols for architecture x86_64:
  "Movement& Entity::AddComponent<Movement>()", referenced from:
      Game::Start() in Game.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)