How to include header file through makefile

Question

I know that there is a flag that can be used in makefile to include a header file in all the files which are being compiled, just like there is a -D flag to include a define

Answer 1

In your compile command, you can use the -include option:

gcc -o main -include hello.h main.cpp 

Answer 2

something like this maybe? include_directories(${CMAKE_CURRENT_SOURCE_DIR}/include)