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This article introduces the relevant knowledge of "what are the namespace characteristics of C++". In the operation of practical cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

1. Namespace characteristics 1. Nesting

We can nest namespace declarations:

Namespace elements {namespace fire {int flame;...} float water;}

If we take a look, we can see that the flame here is in elements::fire, so when we use the parsing operator to use it, it is written as: elements::fire::flame.

Similarly, we can use the using compilation directive to introduce the fire namespace:

Using namespace elements::fire;2. Transfer

And we can also apply using compilation instructions and using declarations to namespaces:

Namespace myth {using Jill::fetch; using namespace elements; using std::cout; using std::cin;}

Suppose we are going to visit Jill::fetch, and since it has been introduced into myth, we can visit it as follows:

Std::cin > > myth::fetch

And the using compilation instructions can be passed, An introduces B, B introduces C, which is equivalent to An also introduces C. For example, when we run using namespace myth;, because elements is introduced into myth, it is equivalent to running both of them at the same time:

Using namespace myth;using namespace elements;3. Alias

We can also create aliases for namespaces, such as:

Namespace my = myth::elements::fire;using my::flame

In the above example, we combine aliases with namespace nesting. In fact, it's a bit like treating a namespace as a special variable.

4. Anonymous namespace

We can also omit the name of the namespace to create an anonymous namespace.

Namespace {int ice; int bandy;}

It is the same as followed by the using compilation instruction, that is, the potential scope of an anonymous namespace is from the declaration point to the end of the declaration area. From this point of view, it is similar to global variables. But because it is anonymous, it cannot be introduced using the using keyword in other files, so it cannot be used in other files, which is somewhat similar to internal static variables in a sense.

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