自动将指向派生类的指针列表转换为指向基类的指针列表 [英] automatically convert list of pointers to derived class to list of pointers to base class

问题描述

让我们说我有一个基类和派生类，以及一个使用指向基类指针的stl向量的函数：

Lets say that I have a base and derived class, and a function that takes an stl vector of pointers to the base class:

class A { public: int x; };

class B : public A { };

void foo(const vector<A*> &va) {
    for (vector<A*>::const_iterator it = va.begin(); it < va.end(); it++)
        cout << (*it)->x << endl;
}

是否可以将指针列表传递给派生类？即：

is there any way to pass a list of pointers to the derived class? ie:

vector<B*> vb;
// ... add pointers to vb ...
foo(vb);

以上内容将导致以下编译器错误：

The above will cause the following compiler error:

error: could not convert ‘vb’ from ‘std::vector<B*>’ to ‘std::vector<A*>’

即使B *可转换为A *。

Even though B* is convertible to A*.

最后，如果有普通指针的解决方案，它也可以与Boost共享指针一起使用吗？

Finally, if there is a solution for plain pointers, will it work with boost shared pointers as well?

推荐答案

std :: vector< B *>和std :: vector< A *> 在技术上不相关。 C ++不允许这样。

std::vector<B*> and std::vector<A*> are technically unrelated. C++ does not allow what you want as such.

一种解决方法……为什么没有 std :: vector< Base *> 并在其中插入 Derived 对象？这就是多态的意义，动态调度等。

A way around...Why not have a std::vector<Base*> and insert into it Derived objects? That is the point of polymorphism, dynamic dispatch et al.

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