16.2.5 Namespaces

C++ namespaces are a facility for expressing a relationship between a set of related declarations such as a set of constants. Namespaces also assist in constraining names so that they will not collide with other identical names in a program. Namespaces were introduced to the language in 1993 and some early compilers were known to have incorrectly implemented namespaces. Here's a small example of namespace usage:

namespace Animals { class Bird { public: fly (); {} // fly, my fine feathered friend! }; }; // Instantiate a bird. Animals::Bird b;

For compilers which do not correctly support namespaces it is possible to achieve a similar effect by placing related declarations into an enveloping structure. Note that this utilises the fact that C++ structure members have public protection by default:

struct Animals { class Bird { public: fly (); {} // fly, my find feathered friend! }; protected // Prohibit construction. Animals (); }; // Instantiate a bird. Animals::Bird b;