Is there any way to include a header file in all C or CPP file automatically? [duplicate]

Answer 1

In the makefile itself directly, you can do a -DFEATURE1_SUPPORTED=1 for it to take effect on all CPP's using it.

Refer to the SO question: Is it possible to define a C macro in a makefile?

Answer 2

Add the appropriate preprocessor option for gcc to your Makefile-s and have a common_feature_header.h header file defining these.

 # in Makefile
 CPPFLAGS+= -include common_feature_header.h

If you just want to define some preprocessor flags, you don't need a common_feature_header.h file, but simply add into your Makefile the following definition

 CPPFLAGS+= -DSOME_FEATURE_FLAG=1 -DSOME_OTHERFEATURE_FLAG=0 \
            -DYET_ANOTHER_THING=2

See also this answer.

P.S. You may want to use remake (notably with its -x option) to debug your Makefile.