C ++ 11是否允许非匿名联合包含静态数据成员? [英] Does C++11 allow non-anonymous unions to contain static data members?

问题描述

在C ++ 11中，我声明以下联合:

In C++11 I declare the following union:

union U4 {
    char c;
    int i;
    static int si;
};

当我使用-std = c ++ 11 -pedantic-errors在g ++ 4.7.0中编译此代码时，出现以下错误(仅进行了少量编辑):

When I compile this code with g++ 4.7.0 using -std=c++11 -pedantic-errors, I get the following errors (with minor editing):

错误:本地类"Union U4"不应具有静态数据成员"int U4 :: si" [-fpermissive]
错误:"U4 :: si"可能不是静态的，因为它是工会的成员

error: local class ‘union U4’ shall not have static data member ‘int U4::si’ [-fpermissive]
error: ‘U4::si’ may not be static because it is a member of a union

据我所知，FDIS(N3242)并未明确 allow 命名联合的静态数据成员.但是我也看不到FDIS在哪里不允许 命名联合的静态数据成员.FDIS重复提到了非静态数据成员"可以完成的工作[第9.5节第1节].相比之下，这表明该标准允许联合的静态数据成员.

The FDIS (N3242) does not explicitly allow static data members of named unions, as far as I can see. But I also don't see where the FDIS disallows static data members of named unions either The FDIS does repeatedly refer to what can be done with "non-static data members" [section 9.5 paragraph 1]. By contrast, that suggests the standard permits static data members of unions.

对于联合的静态数据成员，我没有任何用处.如果需要，我可以使用包含匿名联合的类获得足够接近的效果.我只是想了解标准的意图.

I don't have any use in mind for a static data member of a union. If I needed it I could probably get a close enough effect with a class containing an anonymous union. I'm just trying to understand the intent of the standard.

感谢您的帮助.

推荐答案

是的，这是允许的.该标准的第9节在类，结构和联合中使用 class 一词，除非另有明确说明.对静态工会成员的唯一限制是本地工会(9.4.2/5)和匿名工会(9.5/5).

Yes this is allowed. Section 9 of the Standard uses the word class for classes, structs and unions, unless it explicitly mentions so otherwise. The only restrictions on static union members are for local unions (9.4.2/5) and for anonymous unions (9.5/5).

#include <iostream>

union Test
{
    static int s;   
};

int Test::s;

int main()
{
   Test::s = 1;
   std::cout << Test::s;  
}

LiveWorkSpace 上的输出.请注意，它可以在Clang 3.2上编译，但不能在gcc 4.8.0或Intel 13.0.1上编译.看来这是gcc/Intel错误.

Output on LiveWorkSpace. Note that it compiles on Clang 3.2 but not on gcc 4.8.0 or Intel 13.0.1. It appears this is a gcc/Intel bug.

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