如何在C++中將一個類的對象存儲為另一個類？

std::variant將在C++17或更高版本中實現這一功能（請參閱下面的示例），盡管在某些情況下，您可能會發現只聲明單獨的vector<A>和vector<B>對象更容易。

#include <iostream>
#include <variant>
#include <vector>

class A
{
public:
    A() : _x(0) {/*...*/}
    A(int x) : _x(x) {/*...*/}

    int getX() const {return _x;}

private:
    int _x;
};

class B
{
public:
    B() : _y(0.0f) {/*...*/}
    B(float y) : _y(y) {/*...*/}

    float getY() const {return _y;}

private:
    float _y;
};

int main(int, char **)
{
   std::vector< std::variant<A, B> > v;

   v.push_back(A(777));
   v.push_back(B(3.14159f));

   for (auto item : v)
   {
      const A * a = std::get_if<A>(&item);
      if (a)
      {
         std::cout << "The A object has int value x=" << a->getX() << std::endl;
      }
      else
      {
         const B * b = std::get_if<B>(&item);
         if (b)
         {
            std::cout << "The B object has float value y=" << b->getY() << std::endl;
         }
         else
         {
            std::cout << "Hmm, I'm not sure what item is!" << std::endl;
         }
      }
   }

   return 0;
}