如何区分派生类的对象C ++ [英] How to distinguish objects of derived classes C++

问题描述

看下面的代码:

class A
{
protected:
    int aa = 1;
};

class B : public A
{
private:
    int bb = 2;
public:
    int getbb() { return bb; }
};

class C : public A
{
private:
    int cc = 3;
public:
    int getcc() { return cc; }
};

int main()
{
    std::vector<A> a;
    B b;
    C c;
    a.push_back(b);
    a.push_back(c);

    a[0].getbb(); //getbb() unaccessible;
    a[1].getcc(); //getcc() unaccessible;
}

A是基类. B和C是派生类.我想设置一个向量来保存B或C，并使用向量a来保存A.但是，由于a是包含A对象的向量，因此我无法访问B和C中的方法.反正有什么办法可以使a[0].getbb()和a[1].getcc()工作?

A is the based class. B and C is the derived classes. I want to set a vector to hold either B or C, and use vector a to hold A. However, since a is a vector containing A's objects, I can't access methods in B and C. Is there anyway to make a[0].getbb() and a[1].getcc() work?

推荐答案

您的A向量不能容纳B s或C s，因为它按值存储A，导致<存储B或C时，em>对象切片.特别是，这意味着当您存储B时，仅会存储aa； bb被切开.

Your vector of A is not capable of holding Bs or Cs, because it stores A by value, resulting in object slicing when B or C is stored. In particular, this means that when you store B, only aa gets stored; bb gets sliced away.

为了存储子类而不进行切片，请使用一个指针容器-最好是 smart 指针.

In order to store subclasses without slicing use a container of pointers - preferably, of smart pointers.

如果不进行强制转换，这将无助您访问特定于B或C的功能.解决此问题的一种方法是将>的 virtual 成员函数和C的功能提供给A，并通过B的A类型引用进行调用>或C.

This wouldn't help you access functionality specific to B or C without a cast. One way to solve this problem is to give virtual member functions for B's and C's functionality to A, and make calls through A-typed reference of B or C.

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