为什么我不能在std :: vector中使用抽象类? [英] Why I can not use abstract class in std::vector?
问题描述
我来自那些问题:
- Why can't we declare a std::vector<AbstractClass>?
- abstract classes in std containers
- How to store a vector of objects of an abstract class which are given by std::unique_ptr?
他们都建议我应该改用指针或智能指针.
They all suggested that I should use pointer or smart pointers instead.
据我所知，数据是在std::vector中动态分配的，这意味着std::vector内部存在指针.那么为什么我不能直接使用抽象类呢?为什么我必须对内部使用指针(我指定的指针)才能使用带有std::vector的抽象类.我知道std::vector::resize之类的某些功能将无法使用.但是，std::vector::reserve和std::back_inserter将解决此问题.
As far as I know, Data are dynamically allocated in std::vector which means that there are pointers internally in the std::vector. So why I can not use abstract classes directly? why I have to use pointers(The one I specified) for pointers(the internally) in order to use abstract classes with std::vector. I know some features like std::vector::resize won't work. However, std::vector::reserve and std::back_inserter will solve the problem.
推荐答案
据我所知，数据是在std :: vector中动态分配的，这意味着
std::vector
那是绝对正确的.但是，指针(实际上是非常常见的实现中的两个指针之一)指向类型为T的大小相同的元素数组，而不是指向T的单个元素或其子类型.本质上，指针用于表示数组，而不是引用类或其子类.
That's absolutely right. However, the pointer (actually, one of two pointers in the very common implementation) points to an array of identically-sized elements of type T, not to a single element of T or its subtype. Essentially, the pointer is used to represent an array, not to refer to a class or its subclass.
这就是为什么您需要额外的间接访问级别的原因-数组T[]的元素在没有 slice切片的情况下不能存储T的子类.
That is why you need an extra level of indirection - elements of an array T[] are not capable of storing subclasses of T without object slicing.
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