C ++翻译单元的语法 [英] Grammar of a C++ Translation Unit

问题描述

我的理解是，在很长时间之后，是一个C ++翻译单元，在预处理器运行之后，是一个声明序列（让我提醒任何定义也是一个声明）。

My understanding, for a long time now, was that a C++ translation unit, after the preprocessor has run, is a sequence of declarations (let me remind that any definition is also a declaration).

许多人都在使用这个语句，但没有人曾经给过一个反例。但我自己发现这个例子困扰我：

Many people have argued with this statement but no one has ever given a counterexample. But I myself found this example which troubles me:

int x;       //declaration

;            // ??? EMPTY DECLARATION?

int main()   //dec
{            //la
}            //ration

这与MSVC和online comeau编译良好。我知道标准定义了 空语句 ，但我从来没有听说过空声明。所以，我看到三个选项：

This compiles fine with MSVC and online comeau. I know the standard defines an empty statement but I never heard of an empty declaration. So, I see three options:

• 我的理解正确，标准定义了一个空声明


• 我的理解是正确的，但是标准没有定义空声明，并且上面的翻译是错误的


• 我的理解是不正确的，即一个C ++ TU不是一个声明序列
• 
  

• My understanding is correct and the standard defines an empty declaration
• My understanding is correct but the standard doesn't define empty declarations and the above translation is ill-formed
• My understanding is incorrect, i.e. a C++ TU is not a sequence of declarations

请帮我解开我的疑惑。感谢

Please help me dissolve my doubts. Thanks

推荐答案

在C ++ 0x的当前草稿中允许使用空声明在文件范围（和命名空间范围和其他允许声明的地方），它只是一个分号。它是一个独立的语法实体。

An empty-declaration is allowed in (the current draft of) C++0x at file scope (and namespace scope and other places where a declaration is allowed) and it is just a semicolon. It is a standalone grammatical entity.

在C ++ 03中，不允许只有一个声明的单独的分号。虽然可能会出现一个简单声明可能只能减少到一个分号，但显式规则不允许这样做。

In C++03 a lone semicolon is not allowed where only a declaration is expected. Although it might appear that a simple-declaration might be able to reduce to just a semicolon an explicit rule disallows this.

7 [dcl。 dcl] / 3

7 [dcl.dcl] / 3

在简单声明中，可以省略可选的 init-declarator-list 当声明一个类（第9节）或枚举（7.2）时，即当 decl-specifier-seq 包含 class-specifier 类型说明符与类键（9.1）或枚举说明符。

In a simple-declaration, the optional init-declarator-list can be omitted only when declaring a class (clause 9) or enumeration (7.2), that is, when the decl-specifier-seq contains either a class-specifier, an elaborated-type-specifier with a class-key (9.1), or an enum-specifier.

简而言之，这意味着只有当未省略 decl-specifier-seq 时，才可以省略 init-declarator-list 。

In short this implies that the init-declarator-list can be omitted only when the decl-specifier-seq is not omitted.

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