In what cases and with which objects is the 'using' directive used in C++?

In C++, the using directive is used to simplify access to names from namespaces or to create type aliases.

Main use cases:

1. Importing names from a namespace:

using namespace std; // allows using names from std without the std:: prefix

2. Importing a specific name:

using std::cout; // now you can write cout instead of std::cout

3. Creating type aliases:

using IntVector = std::vector<int>; // alias for the type

The using directive makes reading and writing code easier by reducing the need to write long qualified names.