C++ : what is :: for?

Question

If you go to the accepted answer of this post

Could someone please elaborate on why he uses:

double temp = ::atof(num.c_str());

and

Answer 1

:: is the scope resolution operator. Its use in this scenario, as a unary operator, is to ensure that the name (atof) is always looked up in the global scope -- this can be useful to prevent name hiding from interfering with the lookup.