Re: Make with another make as a prerequisite

[Henrik Carlqvist]

"crjjrc" <crjjrc@gmail.com> wrote:
> Henrik Carlqvist <Henrik.Carlqv...@deadspam.com> wrote:

>> all: myprog
>>
>> myprog: mysrc.c ../lib/mylib.a
>>         gcc -o $@ $^
>>
>> ../lib/mylib.a: FORCE
>>         cd ../lib && $(MAKE)
>>
>> # Used to force some rules to always be compiled
>> FORCE: ;

> I'm not sure I quite understand why it works though.  The prerequisite
> is always checked for out-of-date in and of itself, and not if any of
> the prerequisite's prerequisites cause its commands to be run?  That
> is, even though mylib.a always has its commands run, only when the
> file's modification time (or mysrc.c's) changes is myprog rebuilt?

As the above Makefile doesn't know anything about the prerequisites of
mylib.a it cant tell if anything needs to be compiled to create mylib.a.
Instead it trusts another Makefile to take care of creating mylib.a. The
other Makefile is allways called. Sometimes it does some work, sometimes
it might only say something like "nothing to be done for mylib.a".

Once the other Makefile is finished the Makefile above checks the
timestamps of mylib.a and mysrc.c. If any of those timestamps are newer
than myprog it will rebuild myprog.

regards Henrik
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