C ++ 11 gcc：声明中的显式限定条件？标准参考？ [英] C++11 gcc: explicit qualification in declaration? Standard ref?

问题描述

当下面的C ++ 11程序用gcc 4.7编译时：

When the following C++11 program is compiled with gcc 4.7:

extern int i;
int ::i;

int main()
{
}

gcc抱怨：

error: explicit qualification in declaration of `i`

这是不符合行为吗？

8.3p1似乎表示应该允许：

8.3p1 seems to indicate that it should be allowed:

如果
限定符是全局:: scope解析运算符，则declarator-id引用在全局
命名空间范围中声明的名称。

If the qualifier is the global :: scope resolution operator, the declarator-id refers to a name declared in the global namespace scope.

更新：

来自N3485 8.3p1：

From N3485 8.3p1:

在可选（第7条）decl-specifier-seq（7.1）之后出现一个声明列表。每个声明器包含
正好一个declarator-id;它命名被声明的标识符。在声明符
id中出现的非限定id应该是一个简单的标识符，除了一些特殊函数（12.3,12.4,13.5）的声明和模板特化或部分特化的
声明（14.7 ）。当declarator-id被限定时，
声明将引用限定符
引用的类或命名空间的先前声明的成员（或者在命名空间的情况下，是指该命名空间的内联命名空间集（7.3.1））
或其特殊化;该成员不应仅仅由在声明者id的嵌套名称说明符指定的类或命名空间范围内的使用声明
引入。限定的declarator-id的
nested-name-specifier不能以decltype-specifier开头。 [注意：如果
限定符是global :: scope解析运算符，那么declarator-id是指在全局
命名空间范围中声明的名称。 - end note] declarator-id之后的可选属性说明符seq属于
被声明的实体。

A list of declarators appears after an optional (Clause 7) decl-specifier-seq (7.1). Each declarator contains exactly one declarator-id; it names the identifier that is declared. An unqualified-id occurring in a declarator- id shall be a simple identifier except for the declaration of some special functions (12.3, 12.4, 13.5) and for the declaration of template specializations or partial specializations (14.7). When the declarator-id is qualified, the declaration shall refer to a previously declared member of the class or namespace to which the qualifier refers (or, in the case of a namespace, of an element of the inline namespace set of that namespace (7.3.1)) or to a specialization thereof; the member shall not merely have been introduced by a using-declaration in the scope of the class or namespace nominated by the nested-name-specifier of the declarator-id. The nested-name-specifier of a qualified declarator-id shall not begin with a decltype-specifier. [ Note: If the qualifier is the global :: scope resolution operator, the declarator-id refers to a name declared in the global namespace scope. — end note ] The optional attribute-specifier-seq following a declarator-id appertains to the entity that is declared.

推荐答案

下一句话（在n3337中）：

And the very next sentence says (in n3337):

除了在
类之外的成员函数或静态数据成员的定义外，除了
之外的一个命名空间的函数或变量成员的定义或显式实例化之外，id不应该被定义 b命名空间，或者在其命名空间之外定义显式专门化，或者声明一个
friend函数，该函数是另一个类或命名空间的成员。

A declarator-id shall not be qualified except for the definition of a member function or static data member outside of its class, the definition or explicit instantiation of a function or variable member of a namespace outside of its namespace, or the definition of an explicit specialization outside of its namespace, or the declaration of a friend function that is a member of another class or namespace.

在异常中未提及全局变量的定义。

A definition of a global variable is not mentioned among the exceptions.

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