CODEWITHSUNDEEP
makefile
starrify
starrify

Reputation: 14781

Add dependencies to existing make targets

Condition 0:

Say, I have several source codes, a.c, b.c, ..., z.c, and I want a rule to have each of them compiled. Here is a solution:

%.o: %.c
    $(CC) -c -o $@ $(CFLAGS) $<

Condition 1:

Then I introduce a header c.h used in c.c, and another header e.h used in c.c and e.c, and things become complex:

%.o: %.c
    $(CC) -c -o $@ $(CFLAGS) $<

c.o: c.c c.h e.h
    $(CC) -c -o $@ $(CFLAGS) $<

e.o: e.c e.h
    $(CC) -c -o $@ $(CFLAGS) $<

My question:

Based on the solution of condition 1, is there something like add_dependency in make to simplify the solution and obtain something like the following one?

%.o: %.c
    $(CC) -c -o $@ $(CFLAGS) $<

add_dependency(c.o, c.h e.h)
add_dependency(e.o, e.h)

Or, what do you think is a better solution to condition 1?

EDITED:

Thanks for the kind notice @ctheo :)
Yes I did have a look at autotools and understood that shall satisfy all my needs. However what I'm dealing with is an existing project and its Makefile contains other directives dealing with codes in C++, and I think for now I'd better just modify a few lines instead of port the whole Makefile to autotools, unless I couldn't find a satisfying solution without introducing autotools. :)

Upvotes: 18

Views: 11395

Answers (2)

Crumeniferus
Crumeniferus

Reputation: 117

In addition, the .o files in your example all depend on a .h file with the same stem, so you can generalise that part of your rules too:

c.o: e.h

%.o: %.c %.h
        $(CC) -c -o $@ $(CFLAGS) $<

This way, your “normal” situations are covered entirely by the rule that triggers compilation and your “unusual” situations stand out because those are the only additional rules.

Upvotes: 3

ztik
ztik

Reputation: 3612

At first I did not expected to exist a solution for this. It seemed to me that it was covered by autotools. However, after some search, I found this section of GNU/make manual.

It states that :

One file can be the target of several rules. All the prerequisites mentioned in all the rules are merged into one list of prerequisites for the target.

So there is a solution for your query

c.o: c.h e.h
e.o: e.h

%.o: %.c
        $(CC) -c -o $@ $(CFLAGS) $<

Thanks for insisting. I learned something today :)

Upvotes: 18

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