Directory as a dependency in make rule

Question

Is it possible to specify a directory as a dependency in a Makefile rule? Actually I have a Makefile in a directory and another directory containing all the source files.

.
.
|_ Makefile
|_ src
    |_a.c
    |_a.h

Now I want that whenever I make any change in the src directory i.e. in either of a.c or a.h , a particular rule in my Makefile get called on issuing make command. Something like

Makefile
.
.
.
build: src
    <commands>

clean:
    <commands>

Answer 1

It is possible to have a directory as a dependency, in the sense that if it does not exist it will be rebuilt. It's even possible to arrange a rule that will execute when anything in the directory changes, but it's tricky. And in this case it's almost certainly overkill.

If your intent is ordinary, the usual method will suffice:

OBJ_FILES = foo.o bar.o baz.o
# There are ways to be more succinct, but for now we'll keep it simple.

build: $(OBJ_FILES)
    <commands...>

%.o: src/%.c src/%.h
    <commands for building something.o>

clean: # This should not require prerequisites
    <commands...>