The `using` directive, available in several languages including C# and C++, introduces members of a namespace into the current identifier search scope.
The C++ using directive allows the names in a namespace to be used without the namespace-name as an explicit qualifier. Of course, the complete, qualified name can still be used to improve readability.
// C++ Example:
using std::cout
The C# using directive is used to qualify namespaces and create namespace or type aliases. The scope of a using directive is limited to the file in which it appears.
// C# Example:
using System.Text;
using Project = PC.MyCompany.Project;
Creating an alias for a namespace or a type in C# is called a "using alias directive", and is illustrated in the code sample below:
namespace PC
{
    // Define an alias for the nested namespace. 
    using Project = PC.MyCompany.Project;
    class A
    {
        void M()
        {
            // Use the alias
            Project.MyClass mc = new Project.MyClass();
        }
    }
    namespace MyCompany
    {
        namespace Project
        {
            public class MyClass { }
        }
    }
}
 
     
     
     
     
     
     
     
     
     
     
     
     
     
    