Re: ways of recursing into subdirectory

[Paul D. Smith]

%% "Fairweather, James" <address@hidden> writes:

  fj> I have something like this: 

  fj> SUBDIRS = foo bar 

  fj> all: 
  fj>         for dir in $(SUBDIRS) ; do $(MAKE) -C $$dir; done 

  fj> which works fine, but it's using the shell's for function. 

Actually, this doesn't work fine.  This is the most common method, but
it's poor because it does not handle errors properly.  In the above
method, if one of the subdirectories fails, then make does not stop but
rather continues to run.

If you change the loop to check that the subdirectory failed and stop,
then using "make -k" behaves incorrectly (it still stops when it should
continue).

And, even if you should try to solve that by looking for a "k" in
MAKEFLAGS or somesuch silliness, it still is not ideal because likely
there are a number of directories which _are_ able to be built if
another one fails, and there are also some which can't be.  You'd have
to add a lot of logic to your loop to get this right, and once you
looked at it you'd realize that actually, this is exactly what make
itself is designed to do.  Not to mention that you don't get the full
benefit of parallel builds because you're sequentially building every
directory.

  fj> Also, I have this: 

  fj> SUBDIRS = foo bar 

  fj> ALLDIR          = $(addsuffix .all,$(SUBDIRS)) 

  fj> all: $(ALLDIR) 

  fj> %.all: 
  fj>         $(MAKE) -C $* 

Something like this is the best solution, and this is what I always
use.

Also, don't forget to add:

  .PHONY: all $(ALLDIR)

And of course, if you need to ensure that some directory is built before
others, be sure to add:

  foo.all: bar.all baz.all

etc.

-- 
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