将派生 class 存储到向量 C++

Question

我在将 child class object 存储到向量时遇到问题。我有 parent class

class IngameObject
{
protected:
    bool clickable = false;
};

我有第二个class

class Character : public IngameObject
{
protected:
    bool clickable = true;
};

现在，我正在尝试创建 Character 的新实例并将其存储到向量中。我将矢量定义为

std::vector<IngameObject*> objVector;

创建角色并存储它们的代码是

for(int i = 0; i < 1; i++)
{
     int a = i*32;
     Character *c = new Character(this->holderTextures["texture"], sf::IntRect(a, a, 32, 32), sf::Vector2f(2*a, 10.f));
     std::cout << instanceof<Character>(c) << " TEST" <<std::endl;
     this->objVector.emplace_back( c );
     std::cout << instanceof<Character>(this->objVector.back()) << " TEST" <<std::endl;
}

第一种情况，instance是Character。在 emplace_back 之后，objVector 是实例 IngameObject 的类型，并且 bool clickable 设置为 false。我做错了什么？

编辑 Instanceof 定义为

template<typename Base, typename T>
inline bool instanceof(const T*) {
   return std::is_base_of<Base, T>::value;
}

Answer 1

将派生的 class 存储在 std::vector 中是正确的：问题与多态性或“将派生的 class 存储在向量中”无关：

#include <iostream>
#include <vector>

class IngameObject
{
protected:
    bool clickable = false;
};

class Character : public IngameObject
{
protected:
    bool clickable = true;
};

int main()
{
    std::vector<IngameObject*> objVector;
    
    Character *c = new Character();
    objVector.emplace_back( c );
    
    delete c;

    return 0;
}

问题与你实现有关instanceof

要解决 instanceof 函数，您的 class 需要是多态的。然后，指向基class的指针可以转换为派生class，从而确认它是instanceof基class:

#include <iostream>
#include <vector>

class IngameObject
{
protected:
    bool clickable = false;
    virtual ~IngameObject() = default;
};

class Character : public IngameObject
{
protected:
    bool clickable = true;
};

template<class T, class U>
inline bool instanceof(U* ptr) {
   return nullptr != dynamic_cast<T*>(ptr);
}


int main()
{
    std::vector<IngameObject*> objVector;
    
    Character *c = new Character();
    std::cout << instanceof<Character>(c) << " TEST" <<std::endl;
    objVector.emplace_back( c );
    std::cout << instanceof<Character>(objVector.back()) << " TEST" <<std::endl;
    
    delete c;

    return 0;
}

注意：要使Base多态，它需要至少有一个虚方法。

将派生 class 存储到向量 C++

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