Re: library dependencies SUBDIR problem automake

[Michiel Soede]

Hi John,

Thanks for the fast reply (my mailtool messed up the line-feeds I guess, 
sorry about that).
You were right about the wrong order in SUBDIRS = apps comps (that was a 
type).

Your answers raised some new questions to me:

- non-recursive make, is that the same as just making one big make file that 
will always build
 everything? So I would loose the ability to build (for example) only one 
application, or library?

- isn't there any other way to modify the makefile.am of an application so 
that it will execute the
 makefile's of it's dependend library (components)?

- making a hack so that an application will go BACK into the directories of 
the dependend
 components by adding SUBDIRS = ../comps/comp1 is probably not the way to 
go (and can
 cause infinity recursion loops).

best regards,
Michiel

--------------------------------------------------
From: "John Calcote" <address@hidden>
Sent: Tuesday, August 04, 2009 6:54 PM
To: "Michiel Soede" <address@hidden>
Cc: <address@hidden>
Subject: Re: library dependencies SUBDIR problem automake

> Hi Michiel,
>
> On 8/4/2009 10:01 AM, Michiel Soede wrote:
> > Hi,
> > I have a problem with dependencies to libraries in my build structure.the 
> > directory structure in my project is as follows (roughly):
> >
> > configure.acmakefile.amapps/         makefile.am         app1/ 
> > main.cc               makefile.am       comps/         makefile.am 
> > comp1/               comp1.cc               makefile.am
> > the component makefile generates a library:noinst_LIBRARIES = 
> > libcomp1.alibcomp1a_a_SOURCES = comp1.cc
> > I recurse in all subdirectories, using SUBDIRS:SUBDIRS = apps comps
> > in the comps:SUBDIRS = comp1
> > same for the apps directory.
> > the app1 uses LDADD to link the app with main.cc
> > bin_PROGRAMS = app1app1_SOURCES = main.ccapp1_LDADD = 
> > $(top_builddir)/comps/comp1/libcomp1.a
> > Now when I call make at the root, everything is build correctly.
> > But when I cd into apps/app1/ and call make, I have problems with:
> > - if comp1 was not made before (e.g. from the root), make will fail  (no 
> > rule to make libcomp1.a)
> > - if I did make the library at the root, it is not recompiled 
> > automatically when  I modify comp1.cc
> > .. any ideas on these problems?
> The lack of proper text wrapping on your message made it a bit difficult 
> to see your directory structure, but I think I've sorted it out, based on 
> your other comments:
>
> configure.ac
> makefile.am
> apps/
>   makefile.am
>   app1/
>     main.cc
>     makefile.am
> comps/
>   makefile.am
>   comp1/
>     comp1.cc
>     makefile.am
>
> According to your makefiles, app1 is dependent on comp1 (app1_LDADD = 
> .../libcomp1.a), but comp1 is not built as a sub-component (sub-directory) 
> of app1. Thus, (I believe you are saying) when you build from the project 
> root, everything is fine, but when you build from the app1 directory, 
> comp1 doesn't get built, and thus the app1 build fails. Is this correct?
>
> A recursive build system must be designed to build component dependencies 
> first before building the components. Thus, one limitation of a recursive 
> build system is that it rather defines (or at least constrains) the 
> directory structure that you must use. To get comps to be built before 
> apps from within the app1 directory, you must build the comps directory 
> structure from within the app1 directory.
>
> I recognize that applications 2-n may also use components 1-n, so you have 
> a problem here, and the only way around it is to use a non-recursive build 
> system. That is, you can place all of your build logic in the top-level 
> Makefile.am file using relative paths, and then the makefile dependencies 
> will be properly structured for you by Automake:
>
> Makefile.am:
> = = = = = = = = = = =
> bin_PROGRAMS = app1 app2 app3 ...
> app1_SOURCES = apps/app1/main.cc
> app2_SOURCES = apps/app2/...
> ...
>
> noinst_LIBRARIES = libcomp1.a libcomp2.a libcomp3.a ...
> libcomp1_a_SOURCES = comps/comp1/comp1.cc
> libcomp2_a_SOURCES = comps/comp2/...
> ...
>
> app1_LDADD = libcomp1.a
> = = = = = = = = = = =
>
> I also noted that you had
>
> SUBDIRS = apps comps
>
> in your top-level Makefile.am file. This is wrong - the comps hierarchy 
> should be built before the apps hierarchy, or else there will still be no 
> libraries in the comps hierarchy for the apps to link against, unless 
> you've manually built the comps directory first, and then attempted to 
> build from root.
>
> Regards,
> John