为什么不调用虚函数？ [英] Why is virtual function not being called?

问题描述

//GUITEXT
class guitext : public entity {
public:
    guitext(graphics *gfx, std::string _text, float _x, float _y, 
        float _size, float timeToLive);
    bool update(float deltaTime, gameworld *world);
    void draw(graphics *gfx);
};

void guitext::draw(graphics *gfx) { printf("draw"); }

//ENTITY

class entity {
public:
    virtual bool update(float deltaTime, gameworld *world) 
        { return false; }
    virtual void draw(graphics *gfx) { }
};

//GAMEWORLD

void gameworld::addEntity(entity e) { entitys.push_back(e); }

//MAIN 

for(int i = 0; i < (int)entitys.size(); i++) { entitys[i].draw(gfx); }

我在我的gameworld类中有一个向量。当我添加一个guitext实体到这个向量，我希望它调用guitext :: draw（）函数。但是基类函数正在被调用。

I have a vector in my gameworld class. When I add push a guitext entity to this vector I expect it to call the guitext::draw() function. But the base class function is being called. What am I doing wrong?

推荐答案

你创建了一个 entity 。这些对象始终有实体。如果你想调用多态性，它们需要是指针或引用。 实体的向量如何存储 guitext ？没有足够的空间，它不知道如何销毁它，等等。

You made a vector of entity. Those objects always have type entity. If you want to invoke polymorphism, they need to be pointers or references. How can a vector of entity store a guitext? There's not enough space, it doesn't know how to destroy it, etc etc.

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