Question

Let’s say I have a makefile with the rule

%.o: %.c
 gcc -Wall -Iinclude ...

I want *.o to be rebuilt whenever a header file changes. Rather than work out a list of dependencies, whenever any header file in /include changes, then all objects in the dir must be rebuilt.

I can’t think of a nice way to change the rule to accomodate this, I’m open to suggestions. Bonus points if the list of headers doesn’t have to be hard-coded

Answer 1

If you are using a GNU compiler, the compiler can assemble a list of dependencies for you. Makefile fragment:

depend: .depend

.depend: $(SRCS)
        rm -f "$@"
        $(CC) $(CFLAGS) -MM $^ -MF "$@"

include .depend

or

depend: .depend

.depend: $(SRCS)
        rm -f "$@"
        $(CC) $(CFLAGS) -MM $^ > "$@"

include .depend

where SRCS is a variable pointing to your entire list of source files.

There is also the tool makedepend, but I never liked it as much as gcc -MM