MSVC 2017违反了单个翻译单元中的静态初始化顺序 [英] MSVC 2017 violating static initialization order within single translation unit

问题描述

MSVC 2017社区受到了-std=c++17的阻碍:

MSVC 2017 Community with -std=c++17 chokes on the following example:

#include <iostream>

struct TC
{
    static TC const values[];
    static TC const& A;
    static TC const& B;
    static TC const& C;

    int const _value;
};

inline constexpr TC const TC::values[]{ { 42 }, { 43 }, { 44 } };
inline constexpr TC const& TC::A{ values[0U] };
inline constexpr TC const& TC::B{ values[1U] };
inline constexpr TC const& TC::C{ values[2U] };

int main(int, char**) noexcept
{
    std::cout << std::boolalpha
        << "&A == &values[0]? " << (&TC::A == &TC::values[0U]) << "\n" 
        << "&B == &values[1]? " << (&TC::B == &TC::values[1U]) << "\n"
        << "&C == &values[2]? " << (&TC::C == &TC::values[2U]) << "\n";
    return 0;
}

预期的输出为:

&A == &values[0]? true
&B == &values[1]? true
&C == &values[2]? true

gcc和clang都产生了什么，但是MSVC提供了:

Which is what both gcc and clang produce, but MSVC gives:

&A == &values[0]? true
&B == &values[1]? false
&C == &values[2]? false

如果删除_value成员并且没有用户定义的构造函数，则

MSVC确实会给出正确的结果.

MSVC does give the correct results if the _value member is removed and there is no user-defined constructor.

由于所有这些都在一个翻译单元中，因此我的理解是，这属于 部分排序的动态初始化 :

As all of this is within a single translation unit, my understanding is that this falls under Partially-ordered dynamic initialization:

2)部分排序的动态初始化，适用于所有 不是隐式或显式实例化的内联变量 专业化.如果在订购前定义了部分订购的V或 在每个翻译单元中部分排序的W，V的初始化 在W初始化之前进行排序(或在-之前发生，如果 程序启动一个线程)

2) Partially-ordered dynamic initialization, which applies to all inline variables that are not an implicitly or explicitly instantiated specialization. If a partially-ordered V is defined before ordered or partially-ordered W in every translation unit, the initialization of V is sequenced before the initialization of W (or happens-before, if the program starts a thread)

我无法使用函数来确保初始化顺序，因为我需要constexpr值和 constexpr引用它们.

I cannot use a function to ensure initialization order as I require constexpr values and constexpr references to them.

问题是，这里的MSVC 违反了标准*，对吗?

So the question is, MSVC is in violation of the standard* here, correct?

*当然 cppreference.com 不是标准"，但我假设其中的信息是正确来源的.

*Of course cppreference.com isn't "the standard", but I'm assuming that the information there is correctly sourced.

推荐答案

我将相同的问题隔离到这个简单的示例中:

I isolate the same problem to this simpler example:

#include <iostream>

int values[3];
constexpr int& v{ values[1] };

int main()
{
    std::cout << &v << ", " << &values[1] << "\n";
    return 0;
}

使用最新的MSVC 2017社区，其输出为:

which, using latest MSVC 2017 Community, gives output of:

0119D035, 0119D038

如果删除了constexpr，则不会发生此问题.

The problem does not happen if constexpr is removed.

所以我认为这是带有constexpr参考初始化的编译器错误.该引用已初始化为&values[0] + 1个字节，而不是应为的&values[1].

So I think this is a compiler bug with constexpr reference initialization. The reference was initialized to &values[0] + 1 byte, not &values[1] as it should be.

NB.如果不熟悉constexpr参考定义，请请参见此处或

NB. If anyone is not familiar with constexpr reference definitions, see here or here. constexpr enforces that the initializer is an object with static storage duration.

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