[CMake] Linking archives in a sibling directory

[David Cole]

On Thu, Dec 2, 2010 at 5:40 AM, Michael Hertling <mhertling at online.de>wrote:

> On 12/01/2010 06:03 PM, Raymond Wan wrote:
> > Hi Michael,
> >
> >
> > On Thu, Dec 2, 2010 at 01:03, Michael Hertling <mhertling at online.de>
> wrote:
> >> On 12/01/2010 08:18 AM, Raymond Wan wrote:
> >>> Hi all,
> >>>
> >>> I'm having a problem understanding how I can link to an archive in
> >>> another directory which is not a subdirectory. For example:
> >>>
> >>> myproj
> >>>   +-- main
> >>>     +-- CMakeLists.txt
> >>>     +-- source files for main program
> >>>   +-- dir-A
> >>>     +-- CMakeLists.txt
> >>>     +-- source files for sub-program A
> >>>   +-- dir-B
> >>>     +-- CmakeLists.txt
> >>>     +-- source files for sub-program B
> >>
> >> This error is caused by the fact that the directory "dir-A" is outside
> >> the "main" directory tree, so dir-A's binary directory would likewise
> >> be outside main's binary tree, and this is reasonably forbidden when
> >> configuring "main". You might specify dir-A's binary directory in
> >> main/CMakeLists.txt explicitly, e.g.:
> >>
> >> ADD_SUBDIRECTORY(../dir-A ${CMAKE_CURRENT_BINARY_DIR}/dir-A)
> >>
> >> Hence, subprogA_ar will be built within the binary tree's "dir-A".
> >
> >
> > Ah!  I see now.  I didn't realize I could prepend a path like that.  I
> > was trying to find some kind of "ADD_DIRECTORY" command which had this
> > restriction removed.  But then I realized if I'm looking for something
> > like that, there might be a bigger problem in terms of how I'm
> > organizing things...
> >
> >
> >>> myproj
> >>>   +-- main
> >>>     +-- CMakeLists.txt
> >>>     +-- source files for main program
> >>>     +-- dir-A
> >>>       +-- source files for sub-program A
> >>>     +-- dir-B
> >>>       +-- source files for sub-program B
> >>>
> >>>
> >>> Is this what I should have done??
> >>
> >> As an alternative, consider to add a CMakeLists.txt in "myproj"
> >>
> >> CMAKE_MINIMUM_REQUIRED(...)
> >> PROJECT(myproj)
> >> ADD_SUBDIRECTORY(dir-A)
> >> ADD_SUBDIRECTORY(dir-B)
> >> ADD_SUBDIRECTORY(main)
> >>
> >> and subsequently, configure this directory instead of "main".
> >
> >
> > Ah!  I see.  Then is it recommended that this top-level CMakeLists.txt
> > have just these lines, or should I move the ADD_EXECUTABLE, etc. lines
> > here as well?  Or is this really "up to me" and there isn't a
> > suggested paradigm?
>
> Basically, IMO, a CMakeLists.txt with ADD_EXECUTABLE() et al. should be
> placed in the same directory as the related source files unless there's
> a reason not to do so; this makes for modularity and a well organized
> code base. The above-mentioned directory structure with its top-level
> CMakeLists.txt containing just ADD_SUBDIRECTORY() commands keeps the
> modules main, dir-A and dir-B separate with minimal interconnections.
> In the previous structure, e.g., main/CMakeLists.txt had to know that
> dir-A resides in "../dir-A"; now, such information is concentrated in
> the top-level CMakeLists.txt, and the sole reference of main to dir-A
> is the target "subprogA_ar". Due to CMake's capabilities to track the
> dependencies among targets, it doesn't matter where dir-A is placed
> within the project's source tree. So, in short, don't move the
> ADD_EXECUTABLE() etc. to the top-level CMakeLists.txt.
>
> > I guess I chose my first directory layout because the source in a
> > directory (i.e., dir-A) can be several dependencies down and it can
> > even be used by two targets in two different directories.  So, I
> > figured that keeping them all at the "same directory level" would be
> > best.  But it seems what you're suggesting here seems better -- never
> > thought of it; the "myproj" directory has no files in it...just
> > directories right now...
>
> The top-level directory of non-trivial projects should not contain any
> source files, perhaps a config.h header or the like. Usually, there're
> enough things gathering in a project's root, e.g. READMEs, subdirs for
> documentation, resources or CMake stuff, a CMakeLists.txt file ;) etc.
> The sources, however, should be organized in their own subdirectories,
> so the top-level CMakeLists.txt typically contains ADD_SUBDIRECTORY()
> commands along with configurational stuff like setting up compiler
> flags, processing options or investigating the underlying system,
> but no ADD_EXECUTABLE() or the like.
>
> Of course, there're exceptions


Exceptions? I can't think of any... I think you're absolutely correct for
any non-trivial project.



> and probably strong different opinions.
>

If there are, then they're just plain wrong. :-)


Thanks, Michael, for your contributions to the CMake mailing list. You
provide invaluable advice and assistance for many.

Cheers,
David




>
> Regards,
>
> Michael
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