C# Basic Concepts—Fully Qualified Names

Microsoft .NET Framework, ASP.NET, Visual C# (CSharp, C Sharp, C-Sharp) Developer Training, Visual Studio

Fully Qualified Names

Every namespace and type has a fully qualified name, which uniquely identifies the namespace or type amongst all others. The fully qualified name of a namespace or type N is determined as follows.

• If N is a member of the global namespace, its fully qualified name is N.

• Otherwise, its fully qualified name is S.N, where S is the fully qualified name of the namespace or type in which N is declared.

In other words, the fully qualified name of N is the complete hierarchical path of identifiers that lead to N, starting from the global namespace. Because every member of a namespace or type must have a unique name, it follows that the fully qualified name of a namespace or type is always unique.

The following example shows several namespace and type declarations along with their associated fully qualified names.

class A {}    // A
 
namespace X   // X 
{
   class B    // X.B
   {
      class C {}   // X.B.C
   }
   namespace Y     // X.Y
   {
      class D {}   // X.Y.D
   }
}
 
namespace X.Y   // X.Y
{
   class E {}   // X.Y.E 
}