"functional: No such file or directory" error when compiling for Mega

In file included from C:\Users\HP\Desktop\project\WOMEN SAFETY\CODE\CODE.ino:5:0:

C:\Users\HP\Documents\Arduino\libraries\arduino-async-duplex\src/AsyncDuplex.h:3:22: fatal error: functional: No such file or directory

compilation terminated.

exit status 1 Error compiling for board Arduino/Genuino Mega or Mega 2560.

I split your reply to a dedicated thread, since it was unrelated to the subject matter of the thread you originally posted on.

Please post a link (using the chain links icon on the forum toolbar to make it clickable) to where you downloaded the arduino-async-duplex library from. Or if you installed it using Library Manger (Sketch > Include Library > Manage Libraries in the Arduino IDE or Libraries > Library Manager in the Arduino Web Editor) then say so and state the full name of the library.

Note: The async-serial-device library is now called ManagedSerialDevice https://github.com/coddingtonbear/arduino-managed-serial-device

In the ReadMe for the library is says where to download the library for 'functional' if you want to run the ManagedSerialDevice library on an AVR-based Arduino: https://github.com/SGSSGene/StandardCplusplus