模板中sizeof的constexpr不会编译 [英] constexpr for sizeof in template does not compile

问题描述

在Visual C ++ 2012（C ++ 11）中，我收到错误代码

In Visual C++ 2012 (C++ 11) I am getting error for code

template <typename T, T... I>
struct structFoo
{
  static const T sz = sizeof...(I);        (1)
  static constexpr T size = sizeof...(I);  (2)
};

编译器采用行（1），但是抱怨行（2） b $ b'错误C4430：缺少类型说明符 - int。注意：C ++不支持default-int。

the compiler takes the line (1) but complains that the line (2) is an error: 'error C4430: missing type specifier - int assumed. Note: C++ does not support default-int.

为什么？

推荐答案

p> Microsoft Visual Studio 2015之前未对 constexpr 实施支持。

Microsoft did not implement support for constexpr until Visual Studio 2015.

意味着VC ++ 2012是C ++ 11的一个实现，但这是一个大的过度简化。事实上，随着时间的推移，在多个版本中添加了各种语言和库功能;某些C ++ 11功能，不介意C ++ 14，仍然不受支持：

You imply that VC++2012 is an implementation of C++11, but that's a gross oversimplification. In fact, various language and library features were added over time across multiple versions; some C++11 features, never mind C++14, are still not supported:

• https://msdn.microsoft.com/en-us/library/hh567368.aspx #corelanguagetable

• https://msdn.microsoft.com/en-us/library/hh567368.aspx#corelanguagetable

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