I am quite new to PlatformIO and a beginner/basic programmer and currently writing an Arduino - project.
Even after reaseaching i could not find a understandable or working solution for my problem.
I have a main.cpp file and want to include a header file into it. --> Therefore i placed it (header.h and header.cpp) into the /include folder of my project (since it is made to put header-files there) and tried to include it via #include “header.h” in the main.cpp file.
When building, I get the error “undefined reference to” my fuction in the header.h file.
After reaseaching i found out, that the include folder is not gobal and my main file cannot “see” the header but with the build-option “build_flags” in the platformio.ini file, i can include the folder.
But i simply cannot get it to work, since i don’t know what to type exactly.
The syntax should look something like this as far i found out.
[something here] build_flags = -I include
What do i put in the brackets  ?
Do i put in a path instead of include? Is this then computer specific?
Thanks for the help in advance.