为什么用::，例如:: std :: vector来预命名命名空间 [英] why prepend namespace with ::, for example ::std::vector

问题描述

我看过生产代码，例如

  :: std :: vector< myclass> myvec; 
  

我不知道前面的 ::

http://stackoverflow.com/questions/4925148/c-proper-way-to-iterate-over-stl-containers/4925261#4925261\">C++：迭代STL容器的正确方法

解决方案

前导::指的是全局命名空间。假设你说 namespace foo {... 。然后 std :: Bar 指 foo :: std :: Bar ，而 :: std :: Bar 是指 std :: Bar ，这可能是用户的意思。因此，如果您不确定您当前处于哪个命名空间，那么始终包括初始的::可以防止引用错误的命名空间。

I have seen production code such as

::std::vector<myclass> myvec;

I have no idea what the prepending :: mean however - and why is it used?

For an example see:

C++: Proper way to iterate over STL containers

解决方案

The leading "::" refers to the global namespace. Suppose you say namespace foo { .... Then std::Bar refers to foo::std::Bar, while ::std::Bar refers to std::Bar, which is probably what the user meant. So always including the initial "::" can protect you against referring to the wrong namespace, if you're not sure which namespace you're currently in.

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