我一直在使用 Boost 库，在 Boost.Exception 中，我注意到如下代码:
I've been using the Boost libraries, and in Boost.Exception, I've noticed code like the following:
#define BOOST_THROW_EXCEPTION(x) ::boost::throw_exception(x)
只是出于好奇:boost::throw_exception(x)之前的前导::的目的是什么?
Just out of curiosity: what is the purpose of the leading :: before boost::throw_exception(x)?
引用根命名空间.如果您的类或命名空间使用的名称也存在于根目录中，但在某些时候您希望引用根版本，这通常很有用.
To refer to the root namespace. This is often useful if your class or you namespace uses a name which also exists in the root, but at some point you wish to refer to the root version.
例如，如果我在类中重载了 new，但希望在某个时候引用默认(根)new，那么我将使用 ::new 来引用 root new.
For example, if I have overloaded new in my class, but wish at some point to refer to the default (root) new, then I would use ::new to refer to root new.
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