Strange use of const - why does this compile?

Question

I recently found the following function definition in some code I was reviewing:

void func( const::std::string& str )
{
    // Do something...
}

I am surprised that the const::std::string appears to be legal ( it compiles with GCC4.4, GCC 4.8, Clang 3.2 & Intel 13.0.1).

Does the standard specify that const can be used as a namespace?

Answer 1

Does the standard specify that const can be used as a namespace?

No, it does not, because it can't be.

Your code is the same as:

void func( const ::std::string& str );

The first scope resolution operator denotes global namespace.

Answer 2

It is parsed as

const ::std::string& str

where ::std::string is a valid way to refer to std::string.