是否可以指定重复的C ++类范围？ [英] Is it OK to specify a duplicate C++ class scope?

问题描述

可能重复：

blockquote>



我不会希望这个编译，但它是。这是一个编译器错误，还是有一些正确的含义？

  $ g ++ -c scopes.cpp 
 $ cat scopes.cpp 
 class Log {
 public：
 Log（）{} 
 static void fn（）{} 
}; 
 
 void test（）{
 Log :: Log :: Log :: Log :: Log :: Log :: fn（）; 
} 
 
 $ g ++ --version 
 g ++（Ubuntu 4.4.3-4ubuntu5.1）4.4.3 
  

解决方案

是的，这是合法的。类的名称插入到它自己的命名空间中，它被称为 injected-class-name 。从C ++ 03§9/ 2：

[...]插入到类本身的范围内;这称为 inject-class-name 。
为了进行访问检查， injected-class-name 被视为公共成员名。

请注意， Log :: Log 命名类构造函数，它只允许在某些上下文中，但只要结束 Log :: Log :: ... 使用日志（如 fn ），那么它不会命名构造函数。具体来说，§3.4.3.1/ 1a说：

如果 nested-name-specifier code> C ，以及在 nested-name-specifier 之后指定的名称，
在 C ，是 C （第9节）的注入类名，而是认为名称的名称为
类构造函数 C 。这样的构造函数名称只能在类定义之外的构造函数定义
的 declarator-id 中使用。







Possible Duplicate:
Why are redundant scope qualifications supported by the compiler, and is it legal?

I wouldn't expect this to compile but it does. Could this be a compiler bug, or does it have some correct meaning?

$ g++ -c scopes.cpp
$ cat scopes.cpp
class Log {
public:
    Log() { }
    static void fn() { }
};

void test() {
    Log::Log::Log::Log::Log::Log::fn();
}

$ g++ --version
g++ (Ubuntu 4.4.3-4ubuntu5.1) 4.4.3

解决方案

Yes, it's legal. A class's name is inserted into its own namespace, which is called the injected-class-name. From C++03 §9/2:

[...] The class-name is also inserted into the scope of the class itself; this is known as the injected-class-name. For purposes of access checking, the injected-class-name is treated as if it were a public member name.

Note that Log::Log names the class constructor, which is only allowed in certain contexts, but as long as you end the chain of Log::Log::... with something other than Log (such as fn), then it doesn't name the constructor. Specifically, §3.4.3.1/1a says:

If the nested-name-specifier nominates a class C, and the name specified after the nested-name-specifier, when looked up in C, is the injected-class-name of C (clause 9), the name is instead considered to name the constructor of class C. Such a constructor name shall be used only in the declarator-id of a constructor definition that appears outside of the class definition.

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