在C ++ 11中提出的无限制联合是什么？

问题描述

我收集无限制联盟作为在C ++ 11中提出的功能之一。任何人都可以解释这个背后的语义和它提供的优势吗？

I gather unrestricted unions as one of the functionality being put forth in C++11. Can anyone please explain the semantics behind this and the advantages it provides?

推荐答案

维基百科上有一个解释：

There is an explaination on Wikipedia : http://en.wikipedia.org/wiki/C%2B%2B0x#Unrestricted_unions

先搜索询问C ++ 0x功能说明。

Search there first before asking about C++0x features explainations.

无限制联盟

//for placement new
#include <new>

struct Point  {
    Point() {}
    Point(int x, int y): x_(x), y_(y) {}
    int x_, y_;
};
union U {
    int z;
    double w;
    Point p;  // Illegal in C++; point has a non-trivial constructor. 
              //   However, this is legal in C++0x.
    U() { new( &p ) Point(); } // No nontrivial member functions are
                               //implicitly defined for a union;
                               // if required they are instead deleted
                               // to force a manual definition.
};

更改不会破坏任何
现有代码，因为它们只放松
当前

The changes will not break any existing code since they only relax current rules.

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