FAQ 15.05 What are some of the rules for using namespaces?

The following example due to Stroustrup (C++ Programming Language, Third Edition, 1997) illustrates some of the basic ideas.

 namespace X {   int i, j, k; } int k; void f1() throw() {   int i = 0;   using namespace X;  // make names from X accessible   i++;                // local i   j++;                // X::j   k++;                // error: X::k or global k?   ::k++;              // the global k   X::k++;             // X's k } void f2() throw() {   int i = 0;   using X::i;         // Error: i declared twice in f2()   using X::j;   using X::k;         // Hides global k   i++;   j++;                // X::j   k++;                // X::k }