Question

let’s say I’ve got:

target.o: target.h target.c
    gcc $(CFLAGS) -c target.c

But I’d like to get rid of the redundant ‘target.c’.
I know that $< will give target.h, is there an internal macro that will give target.c or should I just rearrange it:

target.o: target.c target.h
    gcc $(CFLAGS) -c $<

However… I seem to recall that $< won’t always return target.c in this case, for example if a change in target.h triggered this rule, then $< would return target.h. So is there any way to do this consistently?

Answer 1

You should just use your second example:

target.o: target.c target.h
    gcc $(CFLAGS) -c $<

$< always evaluates to the first prerequisite; it doesn’t matter which one caused the recipe to be run. For more info, see http://www.gnu.org/software/make/manual/make.html#Automatic-Variables.

If you’re really paranoid, you could always do this (but it’s unnecessary):

target.o: target.c target.h
    gcc $(CFLAGS) -c $(filter %.c,$^)