问题描述
对于C ++名称空间的正确用法，我有些困惑.对我来说，很清楚它们如何帮助避免冲突(名称冲突)，但是对于using关键字，现在还不清楚.我的意思是，假设我有一部分代码放入了名称空间，并创建了一个类，例如
I'm a bit confused concerning proper usage of C++ namespaces. It is clear for me how they can help to avoid conflicts (name collision), but it is not clear anymore when it comes to the using keyword. I mean, suppose I have a part of my code that I put into a namespace, and create a class, say
namespace my
{
class vector { ... };
}
当然，当我使用它时，我不想一直输入my::vector，所以我想使用using namespace my.但是，最终我可能需要std名称空间中的某些内容，然后同时需要using namespace std，但这将使我回到最初的名称冲突问题.
Of course, when I use it, I wouldn't like to type my::vector all the time, so I'd like using namespace my. However, I could eventually need something from the std namespace, and then I want using namespace std at the same time, but this will bring me back to the initial name collision problem.
我知道可以仅导入"我需要的功能，例如using std::set，但是在这种情况下，完全像我一样完全导入标准命名空间std和my命名空间是很自然的. d一直都使用它们.
I know that it is possible to "import" only the functionality that I need, like using std::set, but in this case it seems natural to import both the standard namespace std and my namespace completely as I'd use both of them all the time.
这是否意味着即使我使用名称空间，我仍然应该考虑为我的类型赋予非通用名称吗?还是using namespace是错误的，我应该始终键入my::vector吗?谢谢.
Does this mean that even when I use namespaces I should still think about giving non-common names to my types? Or is using namespace a mistake and I should always type my::vector instead? Thanks.
好吧，我可能应该澄清一下，它比输入更像一个可读性问题.到处都有很多::对我来说真的很奇怪.我知道这是关于品味和习惯的问题，但是.
Well, I should probably clarify that it is more a question of readability than typing. Lots of :: everywhere look really weird to me. I know it's a question of taste and habits, but nevertheless.
推荐答案
是的，它将会带您回到最初的名称冲突问题.这就是为什么您应该谨慎使用using namespace ...;指令，并且仅在源文件中使用，而不在标头中使用.
Yes, it would bring you back to the initial name collision problem. This is why you should use using namespace ...; directives sparingly, and only in source files, never in headers.
不，你不应该.正是为了避免这种情况而发明了命名空间.
No, you shouldn't. Namespaces were invented precisely to avoid this.
如果需要，可以使用using namespace ...;或using ...;指令，直到出现冲突.这意味着，当您要做发生冲突时，您将通过在某些地方显式地将名称加以量化来写出不自然的"代码.
You can, if you want to, use the using namespace ...; or using ...; directives until you get conflicts. This means that when you do have conflicts, you'll end up writing "unnatural" code by explicitly quallifying names in some places.
在实践中，当您处理短名称空间名称(即std)时，您可以一直无时无刻地键入它们.大约一周后，您甚至不会注意到您正在输入它.
In practice, when you're dealing with short namespace names (i.e. std), you can just type them explicitly all the time. After a week or so, you won't even notice you're typing it anymore.
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