Cannot compile any files besides src/main.cpp in project

Just installed PlatformIO and cannot for the life of me get it to compile files placed either alongside main.cpp, in a subdirectory of src (e.g., src/util/uuid.c) or in the libs subdirectory (libs/uuid/src/uuid.c or libs/uuid/uuid.c). When I try to build, they’re ignored and then I get link errors involving functions defined therein.

What am I doing wrong?

Image attached. thank you!

Linker ignores them? And you’re 100% sure those linking errors aren’t because you forgot to mark the functions as extern C linkage in your uuid.h file, in case for usage with C++, like your src/main.cpp file is?

I fixed it by renaming the file to .cpp.