Still struggling with libraries - finds cpp but not c

I have a folder:


ive tried every method, but it doesnt seem to pickup the c files, but the cpp files are found. with c files, i get an undefined reference. as a test, I can #include “blahblah.c” which allows this to compile.

i need to share this project with 3 other microcontrollers and maintain this all in a “common” folder. ive tried lib_dep and all sorts of things inside the ini file from deep, chain, external libs, and so on. Is there a way to maintain the “common” folder structure that is a totally different folder in my repo without needing to copy this all into other folders in the project and still have it recognize the C files?

So, in which file are you including these header files? If you include code which is implemented in a .c file from a .cpp file, do you use the

extern "C" {
   #include "blahblah.h"

directive correctly?