Re: Bug or correct behavior?

[Derek Clegg]

On Feb 5, 2008, at 11:40 AM, Paul Smith wrote:

> On Tue, 2008-02-05 at 11:32 -0800, Derek Clegg wrote:
> > Given this simple makefile
> >
> > start: dir/a.c
> > dir/%.c: %.c | dir ; cp $< $@
> > dir/%.c: foo.h
> > dir: ; mkdir $@
> > a.c foo.h: ; touch $@
> >
> > I'm seeing the following when I run make:
> >
> > touch a.c
> > mkdir dir
> > cp a.c dir/a.c
> >
> > This is surprising; my expectation is that the dependency "dir/%c.:
> > foo.h" would force "foo.h" to be created as well.  Is this a bug or
> > correct behavior?
>
> This is correct.
>
> Pattern rules are not the same as explicit rules: only one pattern  
> rule
> will ever match a given target.  Make goes through them in the order  
> you
> define them and whichever one matches first will be used; the rest  
> will
> be ignored.

I responded to Mike Shal in a similar vein.  If you're correct,  
changing the order of the "dir/%.c:" lines would change the behavior,  
but it doesn't appear to.

> Anyway, I don't think you really want the .c file to depend on the .h
> file, do you?  That's pretty unusual.  You don't need to copy the .c
> file again just because the .h file changes?!?!

This is a trivial makefile for illustration purposes only.  Best not  
to take it literally :-)

Derek