问题覆盖虚函数

问题描述

好吧，我正在编写一个游戏，其中包含一个副驾驶级别（敌人）的矢量，这个游戏将充满儿童课程（goomba，koopa，boss1），当我打电话给我更新时，我需要这样做调用子类各自的更新。我设法创建了一个问题的例子。

Okay, I'm writing a game that has a vector of a pairent class (enemy) that s going to be filled with children classes (goomba, koopa, boss1) and I need to make it so when I call update it calls the childclasses respective update. I have managed to create a example of my problem.

#include <stdio.h>
class A{
    public:
        virtual void print(){printf("Hello from A");}
};

class B : public A{
    public:
        void print(){printf("Hello from B");}
};


int main(){
    A ab = B();
    ab.print();
    while(true){}
}

输出通缉：你好来自B
输出得到：你好A

Output wanted: "Hello from B"Output got: "Hello from A"

如何让它调用B的打印功能？

How do I get it to call B's print function?

推荐答案

多态性仅适用于指针和引用。如果您将 B 分配给 A ，则 A ，您将丢失所有 B 特定信息，包括方法覆盖。这称为切片; B 部分在分配给父类的对象时从对象中切片。

Polymorphism only works on pointers and references. If you assign a B to an A, it becomes an A and you lose all B-specific information, including method overrides. This is called "slicing"; the B parts are "sliced" off the object when it is assigned to an object of a parent class.

另一方面，如果您将 B * 分配给 A * ，则看起来喜欢 A * ，但仍然指向 B ，所以 B - 特定信息仍然存在，并且将使用 B 的虚拟覆盖。

On the other hand, if you assign a B* to an A*, it looks like an A*, but is still really pointing to a B, and so the B-specific information remains, and B's virtual overrides will be used.

尝试：

int main(){
    A* ab = new B();
    ab->print();
    delete ab;
    while(true){}
}

这同样适用于分配a B 到 A& （引用 - A ），例如

The same also applies to assigning a B to an A& (reference-to-A), e.g.

int main(){
    B b;
    A& ab = b;
    ab.print();
    while(true){}
}

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