将基类型的STL容器转换为派生类型是否可以？ [英] Is it ok to cast a STL container with Base type to Derived type?

问题描述

是否可以将STL容器从基本类型转换为派生类型？
例如，我有两个向量。第一个是在Base类的类型，第二个是在Derive类的类型。

Is it ok to cast a STL container from Base type to Derived type ? For example, I have two vectors. First one is in type of a Base class, second is in type of a Derive class.

class Base
{
// Code
};

class Derive : public Base
{
// Code
};

使用

    vector<Base*>*  vec_base = new vector<Base*>;

    // Add some Derive type data to vec_base

    vector<Derive*>* vec_derive = (vector<Derive*>*)(vec_base);

    // Using elements as Derive pointers. Works fine. 

这是否确定？ （它工作正常，但我想得到一些意见）。非常感谢你。

Is this ok ? (It works fine, but I wanted to get some comments about this). Thank you very much.

编辑：根据答案更新。

Updating according to the answers.

说，如果我仔细使用该向量，并且不会使用多继承，并且不会插入除Derive类型以外的对象，是否确定？ （我猜，不是）

Say, If I use that vector carefully, and will not use with multiple-inheritance and will not insert objects other than Derive type, is it ok ? (I guess, it is not)

非常感谢你的答案。

推荐答案

这绝对不行，并且是c风格的掩码错误的示例之一。

This is definitely not ok, and is one of the examples of c-style casts masking errors. "It works for me" is not indicative of well defined behaviour in this instance.

如果你真的想这样做，我建议：

If you really want to do this I'd suggest:

#include <vector>
#include <algorithm>
#include <iterator>

using namespace std;

class Base
{
// Code
virtual ~Base();
};

class Derrive : public Base
{
// Code
};

Derrive *convert(Base * in) {
   // assert here?
   return dynamic_cast<Derrive*>(in);
}

int main() {
    vector<Base*>*  vec_base = new vector<Base*>;

    // Add some Derrive type data to vec_base

    vector<Derrive*>* vec_derrive = new vector<Derrive*>;

    transform(vec_base->begin(), vec_base->end(), back_insert_iterator<vector<Derrive*> >(*vec_derrive), convert);
}

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