Unnamed namespace in C++ primer (P. 791)

 

Concepts

---

• Variables defined in an unnanmed namespace have static lifetime.
• Unlike other namespaces, an unnamed namespace is local to a particular file and never spans multiple files.
• Names defined in an unnamed namespace are used directly.
• If an unnamed namespace is defined at the outermost scope in the file, then names in the unnamed namespace must differ from names defined at global scope.

  int i;  // global declaration for i
  namespace{
      int i;
  }
  // ambiguous:defined globally and in an unnested, unnamed namespace.
  i = 10;

• The use of file static declarations is deprecated by the C++ standard. File statics should be avoided and unnamed namespaces used instead.

 

Static and Unnamed namespace

The keyword static applies only to the variables declarations and functions, not to the user-defined types.