c - Add compiler option without editing Makefile

Question

I should compile a program written in C through a Makefile. I should insert into the Makefile, some option, for instance: -O2, -march=i686. How can I insert this option in the Makefile without writing into it?

Answer 1

You should use a macro like CFLAGS. Check out GNU GCC documentation.

Something like this should work:

CFLAGS := $(CFLAGS) -O2 -march=i686

Or, if you prefer not to modify the makefile use:

make CFLAGS='-O2 -march=i686' 

The other options will be picked up automatically though. See overriding variables.