如何在向量中存储不同类型的对象

Question

I have three classes that inherit from the class component. In class Computer I want to store objects of these 3 classes in a vector.

class Component {
public:
    double price;
    virtual void show() {
        std::cout << "Price: " << this->price << std::endl;
    }
};

class CPU : public Component {
public:
    double price;
    CPU(double price){ this->price = price; }
    void show() {
        std::cout << "CPU Price: " << this->price << std::endl;
    }
};

class RAM : public Component {
public:
    double price;
    RAM(double price){ this->price = price; }
    void show() {
        std::cout << "RAM Price: " << this->price << std::endl;
    }
};

class SSD : public Component {
public:
    double price;
    SSD(double price){ this->price = price; }
    virtual void show() {
        std::cout << "RAM Price: " << this->price << std::endl;
    }
};

class Computer : public Component {
public:
    std::vector<Component*> vec;
    void show() {
        for (auto el: vec) {
            std::cout << el->price << std::endl;
        }
    }
};

But when I try to do it I see the garbage there:

Computer c;
c.vec.push_back((Component*)new RAM(10));
c.show(); // garbage
std::cout << c.vec[0]->price << std::endl; // garbage

I read a few questions about this on the stackoverflow, but still don't understand what I'm doing wrong.

Answer 1

The problem is that you're declaring a double price; in each subclass. This creates separate fields, ie RAM::price and SSD::price , in addition to Component::price . Thus, when you construct a new RAM(10) , it only assigns 10 to RAM::price , and not Component::price . That's why you're getting garbage.

To fix, simply remove all those extra declarations.

Also, to aid with properly deleting those pointers you've created, I'd highly suggest using a vector of smart pointers (probably std::vector<std::unique_ptr<Component>> ). Then you could just:

c.vec.push_back(std::make_unique<Component>(new RAM(10)));

and use it as normal; the pointers will get delete d when the vector is destructed.