Namespace in C++

• A namespace allows us to group related functions, classes, variables, and other declarations under a specific name.
• It is used to organize code and avoid name conflicts, especially in large projects or when integrating multiple libraries.

Defining a Namespace

• Define a namespace using the namespace keyword.

  namespace MyNamespace {
      int add(int a, int b) {
          return a + b;
      }
  
      class MyClass {
      public:
          void display() {
              std::cout << "Inside MyNamespace::MyClass" << std::endl;
          }
      };
  }
  

• The function add and class MyClass are part of MyNamespace.

Using a Namespace

1) Fully Qualify Names: Use the namespace name as a prefix:

int result = MyNamespace::add(3, 4);
MyNamespace::MyClass obj;
obj.display();

2) using Keyword: Use the using keyword to avoid prefixing each identifier with the namespace:

using namespace MyNamespace;
int result = add(3, 4);  // No need for MyNamespace::
MyClass obj;
obj.display();

3) Selective Use: We can bring specific members of a namespace into scope:

using MyNamespace::add;
int result = add(3, 4);

Anonymous Namespaces

• An anonymous namespace is a namespace without a name.
• It is used to limit the visibility of its contents to the file in which it is declared.

  namespace {
      int secret() {
          return 42;
      }
  }
  

• The function secret is only accessible within the file where it's defined.
• This is same as making the function static.