不完全类型的静态字段 - 是否合法？ [英] Static field of an incomplete type - is it legal?

问题描述

在C ++中类定义合法的时候，声明一个类型的静态字段是不完整的吗？例如：

Is declaring a static field of a type that is incomplete at the moment of the class definition legal in C++? For example:

Foo.h：

class Foo
{
public:
  // ...
private:
  class Bar;
  static Bar something;
};

Foo.cpp：

class Foo::Bar
{
  // ...
};

Foo::Bar Foo::something;

// some more code

编译器似乎接受它，没有看到应该拒绝的理由，但标准对这种情况说了什么？我真的很感谢有人给出了标准的直接引用，最好是从旧的（从2003年开始）。

Compilers seem to accept it, and I don't see a reason for which it should be rejected, but what does the standard say about such situation? I'd really appreciate someone giving a direct quote from the standard, preferably from the "old" one (the one from 2003).

推荐答案

是的，你所做的是特别允许的（§9.4.2/ 2）：静态数据成员在其类定义中的声明不是一个定义，可能是一个不完整的类型，而不是cv-qualified void。

Yes, what you're doing is specifically allowed (§9.4.2/2): "The declaration of a static data member in its class definition is not a definition and may be of an incomplete type other than cv-qualified void."

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