What's the purpose of a leading “::” in a C++ method call

Question

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_exceptio         


        

Answer 1

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.

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.