rosserial setup done, 1st arduino code fails with cstring error

i’ve done the complete Arduino setup and connected it to a Rasberry Pi 4, it’s working fine,
but when i configure it with ROS by installing the RosSerial library, setup succeeds,

finally when i code any examples of ros_lib
they all fail with this following error message
In file included from /home/ubuntu/arduino-1.8.13/libraries/ros_lib/std_msgs/Time.h:7:0,
from /home/ubuntu/arduino-1.8.13/libraries/ros_lib/ros/node_handle.h:40,
from /home/ubuntu/arduino-1.8.13/libraries/ros_lib/ros.h:38,
from /home/ubuntu/arduino-1.8.13/libraries/ros_lib/examples/HelloWorld/HelloWorld.pde:6:
/home/ubuntu/arduino-1.8.13/libraries/ros_lib/ros/msg.h:40:10: fatal error: cstring: No such file or directory
compilation terminated.
exit status 1
Error compiling for board Arduino Uno.

A link to that library would have helped.

As the example still uses the outdated pde extension I guess the library was developed for an ancient version of the IDE and used some undocumented feature which isn't available anymore. But that's a lot of guessing.

Arduino Rosserial Error Solution (#include -cstring-) - YouTube check this. My probelm was solved