CPP Namespace

What is namespace?

• Namespaces are used to reduce the chance of class name conflicts.
• Namespaces notations are similar in some ways to classes.
• Items declared within the namespace are owned by the namespace.
• Namespaces can be nested within other namespaces.
• There a several ways to denote whatever namespace:

  Giving namespace statement outside the main function, is a global notation that applies to all classes and functions.

  // my first program in C++
  #include <iostream>
  using namespace std; // Notation that applies to all classes and functions
  int main ()  {
    cout << "Hello World!";
    return 0;
  }

  Giving namespace statement inside {} braces, will cause that the namespace can only be used by statements inside those braces.

  #include <iostream>
  int main()  {
   using namespace std; // only for the code inside the braces
   cout << "Hello there.\n"; // \n results in a new line
   return 0;
  }

  Giving namespace statement inside {} braces that is selective on which function to use, will cause that the function(s) in the namespace can only be used inside those braces.

  #include <iostream>
  int main()  {
     using std::cout; // only for the code inside the braces
                      // and the selected function(s)
   cout << "Hello there.\n"; // \n results in a new line
   return 0;
  }

  Giving namespace given directly on the function(s) to use.

  #include <iostream>
  int main()  {
   // Directly on selected function(s)
   std::cout << "Hello there.\n"; // \n results in a new line
   std::cout << "Hello there.";
   std::cout <<  std::endl;  // std::endl results in a new line
   return 0;
  }

  Creating a Namespace:

  namespace Window
  {
      void move( int x, int y) ;
  
      class List
      {
          // ...
      }
  }
  

• All the elements of the standard C++ library are declared within what is called a namespace, which has the name std.
• You can create many occurrences of a named namespace.
• These multiple occurrences can occur within a single file or across multiple translation units.
• When this occurs, the separate instances are merged together by the compiler into a single namespace if they have the same name.