为什么 MSVC 2019 在以三元形式返回静态大小的数组时会失败？

Question

我正在尝试将一些 library code 和运行编译成错误；我简化了示例，我有以下 MVCE，它无法使用 MSVC 2019 进行编译，并出现错误

error C2440: 'return': cannot convert from 'const char *' to 'const char (&)[20]'

static constexpr const char somethingWeird[] = "Well, that's odd...";
void fail() { throw 0; }

// This doesn't work
constexpr const char(&checkNullTerminatedGood(const char(&a)[20]))[20]{
  return a[19] == char(0) ? decltype(a)(a) : (fail(), decltype(a)(a));
}
static constexpr const auto somethingElseNew = checkNullTerminatedGood(somethingWeird);

当我将三元运算符转换为适当的 if 语句时，代码编译得很好：

static constexpr const char somethingWeird[] = "Well, that's odd...";
void fail() { throw 0; }

// This works
constexpr const char(&checkNullTerminatedGood(const char(&a)[20]))[20]{
  if (a[19] == char(0)) {
    return decltype(a)(a);
  } else {
    return (fail(), decltype(a)(a));
  }
}
static constexpr const auto somethingElseNew = checkNullTerminatedGood(somethingWeird);

这是 MSVC 中的错误吗？第一个片段使用 GCC 和 Clang 编译。

Answer 1

googling shows this is know problem 的一小部分声称已修复（但事实并非如此）。

C++ Overly aggressive decay of static array to pointer in ternary operator - Developer Community

Solution

by Leo Zhang [MSFT] Sep 07, 2017 at 02:35 AM

Thank you for your feedback! This issue has been fixed and it will be available in the next update to Visual Studio 2017. Thank you for helping us build a better Visual Studio!”

为什么 MSVC 2019 在以三元形式返回静态大小的数组时会失败？

Why does MSVC 2019 fail when returning a statically-sized array in a ternary?

c++

language-lawyer

Solution