未定义的vtable引用(C++)

Question

我正在为我的sfml游戏制作一个Entity类,但我无法理解为什么下面的代码无法编译.我收到一个undefined reference to vtable in Entity错误.

这是头文件:

#ifndef ENTITY_H
#define ENTITY_H
#include <string>
#include <SFML/System/Vector2.hpp>
#include <SFML/Graphics/Rect.hpp>
#include <SFML/System/Time.hpp>

class Entity
{
public:
        Entity(std::string id, sf::Vector2f position, float rotation );
        virtual ~Entity() = 0;
        virtual sf::FloatRect getBoundingRect() const;
        virtual float getRadius() const;
        void UpdateVelocity(sf::Time);
        void UpdatePosition(sf::Time);
        void Update(sf::Time);
        float getRotation() const;
        sf::Vector2f getPosition() const;
        sf::Vector2f getVelocity() const;
        sf::Vector2f getAcceleration() const;


private:
        std::string mId;
        sf::Vector2f mPosition;
        float mRotation;
        sf::Vector2f mVelocity;
        sf::Vector2f mAcceleration;
};

#endif // ENTITY_H

这是cpp文件:

#include "../include/Entity.h"

Entity::Entity(std::string id, sf::Vector2f position, float rotation)
        : mId(id)
        , mPosition(position)
        , mRotation(rotation)
{
}

Entity::~Entity()
{
}


void Entity::UpdateVelocity(sf::Time dt)
{
        mVelocity += mAcceleration;
}

void Entity::UpdatePosition(sf::Time dt)
{
        mPosition += mVelocity;
}

void Entity::Update(sf::Time dt)
{
        UpdateVelocity(dt);
        UpdatePosition(dt);
}

float Entity::getRotation() const
{
        return mRotation;
}

sf::Vector2f Entity::getPosition() const
{
        return mPosition;
}

sf::Vector2f Entity::getVelocity() const
{
        return mVelocity;
}

sf::Vector2f Entity::getAcceleration() const
{
        return mAcceleration;
}

任何帮助深表感谢!

Answer 1

您缺少一些虚拟方法的实现:

    virtual sf::FloatRect getBoundingRect() const;
    virtual float getRadius() const;

如果您不希望您的Entity类实现这些,请将它们声明为纯虚拟:

    virtual sf::FloatRect getBoundingRect() const = 0;
    virtual float getRadius() const = 0;

请注意,正如@JoachimIsaksson评论的那样,您是否需要将析构函数设置为纯虚拟,这一点并不十分明显.您已为它提供了一个空实现,但仍需要派生类型来实现它.值得考虑的是你是否需要它是纯虚拟的.