This repository contains the source code for the ROS Client Library for C++ package, included with a standard install of any ROS 2 distro.
rclcpp provides the standard C++ API for interacting with ROS 2.
#include "rclcpp/rclcpp.hpp" allows use of the most common elements of the ROS 2 system.
The link to the latest API documentation can be found on the rclcpp package info page, at the ROS Index.
The ROS 2 tutorials Writing a simple publisher and subscriber. and Writing a simple service and client contain some examples of rclcpp APIs in use.