Commonly used messages in ROS. Includes messages for actions (actionlib_msgs), diagnostics (diagnostic_msgs), geometric primitives (geometry_msgs), robot navigation (nav_msgs), and common sensors (sensor_msgs), such as laser range finders, cameras, point clouds.
The operator+ doesn't actually increment, since it references the wrong datachar (the non-incremented one). This was found while debugging https://github.com/ros-planning/moveit_ros/issues/505