按类型对std :: vector进行排序 [英] Sort a std::vector by type

问题描述

我在观看 http：// channel9 .msdn.com / Events / GoingNative / 2013 / Writing-Quick-Code-in-Cpp-Quickly 和大约36分钟，他们谈论了按照元素类型对集合进行排序的好处，如果你要去

I was watching http://channel9.msdn.com/Events/GoingNative/2013/Writing-Quick-Code-in-Cpp-Quickly and around min 36, they talk about the benefits of sorting a collection by the type of its elements if you are going to be calling virtual methods on them.

So given

Base {};
class Der1：public Base {};
class Der2：public Base {};
class Der3：public Base {};

vector< Base *> myVector;

class Base {}; class Der1 : public Base {}; class Der2 : public Base {}; class Der3 : public Base {}; vector<Base *> myVector;

如何排序 myVector 每种类型的元素都是adjecent的方式？

How could you sort myVector in such a way that the elements of each type are all adjecent?

有没有办法做到这一点，而不使用虚函数来标识每个派生类型？ （可能使用 typeid ？）

Is there any way to do that without using a virtual function in order to indentify each derived type? (Maybe using typeid?)

推荐答案

=http://en.cppreference.com/w/cpp/types/type_index> type_index 。您从 typeid 运算符返回的 type_info 对象构造一个。它是一个具有重载的关系运算符的类，具有良好定义的顺序，因此它在关联容器等中用作关键类型。

You can use type_index for this. You constructing one from a type_info object that's returned from typeid operator. It's a class with overloaded relational operators with well defined ordering, so that it is useful as a key type in associative containers and alike.

这是一个例子：

#include <typeinfo>
#include <typeindex>
#include <vector>
#include <algorithm>
#include <iostream>

struct Base {
    virtual ~Base() {}
    virtual const char* who() = 0;
};
struct D1 : Base { const char* who() { return "D1\n"; } };
struct D2 : Base { const char* who() { return "D2\n"; } };
struct D3 : Base { const char* who() { return "D3\n"; } };

int main()
{
    std::vector<Base*> vec { new D2, new D1, new D3, new D3, new D1, new D2 };
    std::sort( vec.begin(), vec.end(),
    [](const Base* p1, const Base* p2)
    {
        return
            std::type_index(typeid(*p1)) <
            std::type_index(typeid(*p2));
    });

    for (auto p : vec) { std::cout << p->who(); }
}

输出为：

D1
D1
D2
D2
D3
D3

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