Re: under the explained algorithm of re-reading timestamps, how to deal with this common situation?

[Lane Schwartz]

On Tue, Apr 3, 2012 at 9:24 AM, Mark Galeck (CW) <address@hidden>wrote:

> Hello,
>
> I think I understand finally how make works, thanks to Paul's excellent
> explanation (being better than the manual's :) )
>
> So then this does not work, even with the empty recipe, it won't work,
> because make figures out that "foobar.h" could not possibly get updated.  I
> touch foobar.y, but foobar does not get updated.
>
> This is a problem, because this represents a common scheme, I think.  How
> do you deal with this situation Paul (so that it "works").
>
>
> foobar is a goal that depends on dynamically generated prerequisites such
> as subdir/foobar.h.  At first build after clean, the prerequisites and the
> rules to depend on them do not exist, so we need something else to
> "bootstrap" on, that's where target "resources" is needed. resources,
> creates the foobar.h dynamically in a subdirectory.  The rule for foobar
> then, creates an additional dynamically generated dependency (like
> explained in the manual) on subdir/foobar.h - this dependency is used in
> the next build.  I simplified that step for this example, so that rule is
> there to begin with, but I am just explaining the "origin" of what I am
> trying to do - Paul always asks for that.
>
> So here is the smallest example, with the origin explained as above:
>
>
> In Makefile:
>
>
> .PHONY: resources
> resources:
>        $(MAKE) -C subdir foobar.h
>
> subdir/foobar.h: ;  # does not matter
>
> foobar: subdir/foobar.h | resources
>        touch $@
>
>
> In subdir/Makefile:
>
>
> foobar.h: foobar.y
>        touch $@
>
>
>
> So, what is the "canonical" way to handle this common situation?
>

Mark,

Is there a reason that the following won't work?

subdir/foobar.h:
       $(MAKE) -C subdir foobar.h

foobar: subdir/foobar.h
       touch $@


In subdir/Makefile:


foobar.h: foobar.y
       touch $@


Cheers,
 Lane