6 Basic concepts [basic]

6.3 Scope [basic.scope]

6.3.6 Namespace scope [basic.scope.namespace]

1
#
The declarative region of a namespace-definition is its namespace-body.
Entities declared in a namespace-body are said to be members of the namespace, and names introduced by these declarations into the declarative region of the namespace are said to be member names of the namespace.
A namespace member name has namespace scope.
Its potential scope includes its namespace from the name's point of declaration ([basic.scope.pdecl]) onwards; and for each using-directive that nominates the member's namespace, the member's potential scope includes that portion of the potential scope of the using-directive that follows the member's point of declaration.
[ Example
: 
namespace N {
  int i;
  int g(int a) { return a; }
  int j();
  void q();
}
namespace { int l=1; }
// the potential scope of l is from its point of declaration to the end of the translation unit

namespace N {
  int g(char a) {   // overloads N​::​g(int)
    return l+a;     // l is from unnamed namespace
  }

  int i;            // error: duplicate definition
  int j();          // OK: duplicate function declaration

  int j() {         // OK: definition of N​::​j()
    return g(i);    // calls N​::​g(int)
  }
  int q();          // error: different return type
}
— end example
 ]
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A namespace member can also be referred to after the ​::​ scope resolution operator ([expr.prim]) applied to the name of its namespace or the name of a namespace which nominates the member's namespace in a using-directive; see [namespace.qual].
3
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The outermost declarative region of a translation unit is also a namespace, called the global namespace.
A name declared in the global namespace has global namespace scope (also called global scope).
The potential scope of such a name begins at its point of declaration ([basic.scope.pdecl]) and ends at the end of the translation unit that is its declarative region.
A name with global namespace scope is said to be a global name.