How to include *project root* headers compiling with GCC C++ compiler?

Question

How to include headers located in project root compiling with GCC C++ compiler?
I want to tell GCC compiler to search for some header files in project root.
I do NOT want to make changes in code and use relative paths in #include directives - e.g. #include "../../myheader.h"
I compile source code I do not own and I do not want to maintain own version.
I do NOT want to specify absolute include path e.g. g++ -c -IC:\root_project_folder .. for obvious reasons.
I have tried: g++ -c -I .., g++ -c -I/ .. and g++ -c -I"/" .. but it does not work.

Please advise.

root_project_folder
|--myheader.h
  |--src_folder
    |-prog.cpp

Answer 1

The symbol for the current directory is ..

You're looking for -I.