Imports

Header File

The header file is the file to be imported. In general, the header file defines all able imported. For instance, the class Vector has its functions defined in Vector.cpp but its declaration in the header file Vector.h.

Modules

Due to various problems and limitations of header files, C++20 adopted modules where the interface declaration and definiton are in the same .cpp file.

Namespaces

A namespace (namespace) can be defined to isolate code so that their names don’t conflict with the global namespace.

Here, ns is a namespace so that int are not in conflict by requiring the double colon syntax ns::int.

namespace ns {
  class int {
    ...
  };
}

int main() {
  ns::int var;
}

Global Namespace

A namespace is imported into the global namespace by the using statement,

using std // Use all of std
using std::cout // Use only std::cout