cppreference.com > C/C++ Keywords > namespace namespace Syntax:
      namespace name {
      declaration-list;
      }
The namespace keyword allows you to create a new scope. The name is optional, and can be omitted to create an unnamed namespace. Once you create a namespace, you'll have to refer to it explicitly or use the using keyword. Example code:
       namespace CartoonNameSpace {
         int HomersAge;
         void incrementHomersAge() {
           HomersAge++;
         }
       }
       int main() {
         ...
         CartoonNameSpace::HomersAge = 39;
         CartoonNameSpace::incrementHomersAge();
         cout << CartoonNameSpace::HomersAge << endl;
         ...
       }
Related topics: using