简单的问题，这是有效的 C++：
class Foo
{
void Foo::doSomething();
};
问题的要点：在类声明中，在方法名称之前重复使用类名和双冒号是否有效？
我在使用 g++ 4.2.3 编译执行此操作的代码时遇到问题。 在深入研究和更改代码之前，我希望在这里看到对描述语法的引用。 或者降级编译器； 这确实是使用 g++ 3.3.6 构建的。
我得到的错误（大致）是：
Foo.h:3: error: extra qualification ‘Foo::’ on member ‘doSomething’
我用谷歌搜索了，但无法想出一些东西。 我没有标准，即使有，也可能需要很长时间才能找到权威的东西。 我不是 C++ 语言律师。
Simple question, is this valid C++:
class Foo
{
void Foo::doSomething();
};
The point of the question: is that repeated use of the class name and double colon before the method name valid inside the class declaration?
I'm having issues compiling code that does this using g++ 4.2.3. I would love to see a reference to something describing the syntax here, before digging in and changing the code. Or downgrading the compiler; this does build with g++ 3.3.6.
The error I'm getting is (roughly):
Foo.h:3: error: extra qualification ‘Foo::’ on member ‘doSomething’
I did Google, but couldn't come up with something. I don't have the standard, and even if I did it would probably take me quite a while to find anything authoritative. I'm no C++ language lawyer.
发布评论
评论（2）
我查看了标准，第 9.2 节是相关部分。 我对 BNF 不太感兴趣，但我在 BNF 中没有看到任何针对班级成员的内容表明这是允许的。 该标识符在 BNF 中甚至被命名为“unqualified-id”。
G++ 改变了 4.1 版本中的行为，显然很多其他编译器都接受了这一点，但我从未见过使用这种风格，我不知道为什么有人会这样做。 由于它似乎不会在多种编译器上触发错误，因此这种风格可能有一些历史原因，但据我所知，它确实无效。
我通过 Google 找到的唯一好的参考是此页面，它只是尝试解释 G++ 4.1 中的一些更改。
I took a look at the standard, section 9.2 would be the relevant portion. I'm not that great with BNF but I didn't see anything in the BNF for class members that would indicate this was allowed. The identifier is even named "unqualified-id" in the BNF.
G++ changed the behavior in version 4.1, and apparently a lot of other compilers accepted this, but I've never seen this style used and I have no idea why anyone would do it. Since it seems to not trigger an error on a pretty wide variety of compilers, there may be some historical reason for this style, but as far as I can tell it's indeed not valid.
The only good reference I found through Google was this page, which just attempts to explain some of the changes in G++ 4.1.
和丹一样，我查看了标准，但没有得到明确的结果。 我用 Comeau 的在线编译器（被认为是世界上最符合标准的）尝试了你的代码，并得到：
如果您有兴趣进一步解决这个问题，我建议您在 comp.lang.c++.moderated 新闻组，因为那里的 C++ 语言律师比这里多得多。
Like Dan, I looked at the Standard without definitive results. I tried your code with Comeau's on-line compiler (considered the world's most standard compliant) and got:
If you are interested in taking this further, I suggest posting a question on the comp.lang.c++.moderated newsgroup, as there are a lot more C++ language lawyers there than there are here.