[CMake] CMake: using dlopen

[Franck Houssen]

I usually read the doc in a step-by-step mode (going from "small things" to "the next") when a (new) need/question shows up. When I can I try to "push" some notions (this is an example of it !). 
The doc is "vast" which is a good thing but not so easy when trying to read/understand all of it (personal opinion). To me, the doc misses simple illustrative examples like Rainer's one (here again, personal opinion). 

----- Mail original -----

> De: "Eric Noulard" <eric.noulard at gmail.com>
> À: "J Decker" <d3ck0r at gmail.com>
> Cc: "Franck Houssen" <franck.houssen at inria.fr>, "CMake Mail List"
> <cmake at cmake.org>
> Envoyé: Lundi 8 Janvier 2018 10:53:51
> Objet: Re: [CMake] CMake: using dlopen

> Explanations on PRIVATE, PUBLIC, INTERFACE has already been discussed in
> those ML threads:
> https://cmake.org/pipermail/cmake/2017-April/065340.html
> https://cmake.org/pipermail/cmake/2016-May/063400.html

> I guess we need some doc update.
> I did promess contribution and I didn't do it.
> I'll try again.

> 2018-01-08 10:45 GMT+01:00 J Decker < d3ck0r at gmail.com > :

> > On Mon, Jan 8, 2018 at 1:41 AM, Franck Houssen < franck.houssen at inria.fr >
> > wrote:
> 

> > > ----- Mail original -----
> > 
> 
> > > > De: "Rainer Poisel" < rainer.poisel at gmail.com >
> > 
> 
> > > > À: "Franck Houssen" < franck.houssen at inria.fr >
> > 
> 
> > > > Envoyé: Dimanche 7 Janvier 2018 19:34:21
> > 
> 
> > > > Objet: Re: [CMake] CMake: using dlopen
> > 
> 
> > > >
> > 
> 
> > > > Hi,
> > 
> 
> > > >
> > 
> 
> > > > On Sun, Jan 7, 2018 at 7:13 PM, Franck Houssen <
> > > > franck.houssen at inria.fr
> > > > >
> > 
> 
> > > > wrote:
> > 
> 
> > > > > Difference between PUBLIC/PRIVATE has never been clear to me (usually
> > > > > I
> > 
> 
> > > > > always use PUBLIC).
> > 
> 
> > > > > main.cpp includes dlfcn.h and uses it: not sure to get what you meant
> > 
> 
> > > > > (PRIVATE is for templates ? when a header include headers ?)
> > 
> 
> > > >
> > 
> 
> > > > you are looking for the "Transitive Dependencies" feature of CMake:
> > 
> 

> > > OK, I didn't get that. It's more clear to me now. Thanks !
> > 
> 

> > > > *
> > 
> 
> > > > https://cmake.org/cmake/help/v3.0/manual/cmake-buildsystem.7.html#transitive-usage-requirements
> > 
> 
> > > >
> > 
> 
> > > > Generally speaking and from my personal experience, use the
> > 
> 
> > > > target_-commands as much as possible because properties are bound to
> > 
> 
> > > > targets and their dependencies rather than a file/directory structure.
> > 
> 
> > > >
> > 
> 
> > > > So, that means, use target_include_directories(),
> > 
> 
> > > > target_compile_options(), target_compile_definitions(),
> > 
> 
> > > > target_sources(), ... for your targets. The magic keyword to propagate
> > 
> 
> > > > the properties of your targets is target_link_libraries(). Depending
> > 
> 
> > > > on what scope (PRIVATE, PUBLIC, INTERFACE) the properties have been
> > 
> 
> > > > defined using the other target_-commands, the target_link_libraries()
> > 
> 
> > > > command propagates these properties to other targets. E. g.
> > 
> 
> > > >
> > 
> 
> > > > add_library(otherlib SHARED
> > 
> 
> > > > foo.c
> > 
> 
> > > > )
> > 
> 
> > > >
> > 
> 
> > > > target_include_directories(otherlib PRIVATE
> > 
> 
> > > > dirPrivate
> > 
> 
> > > > )
> > 
> 
> > > >
> > 
> 
> > > > target_include_directories(otherlib PUBLIC
> > 
> 
> > > > dirPublic
> > 
> 
> > > > )
> > 
> 
> > > >
> > 
> 
> > > > add_library(mylib SHARED
> > 
> 
> > > > bar.c
> > 
> 
> > > > )
> > 
> 
> > > >
> > 
> 
> > > > target_link_libraries(mylib PRIVATE
> > 
> 

> > > Is this a typo ?
> > 
> 
> > > For the example to work I would have done: target_link_libraries(mylib
> > > PUBLIC
> > > otherLib), no ? (mylib needs only PUBLIC stuff's from otherLib but not
> > > PRIVATE one's). Correct ?
> > 
> 

> > Public is whether it propagates outside of the current target to things
> > that
> > then require 'mylib'
> 
> > private keeps it within that target, has nothing to do with what it's
> > pulling
> > from any linked library.
> 

> > > > otherlib
> > 
> 
> > > > )
> > 
> 
> > > >
> > 
> 
> > > > In this case, mylib will use all PUBLIC or INTERFACE properties of
> > 
> 
> > > > otherlib for its build. Thus, dirPublic will be added to the include
> > 
> 
> > > > directory search path for the compilation of bar.c of mylib. PRIVATE
> > 
> 
> > > > properties will not be propagated. In the above mentioned example,
> > 
> 
> > > > dirPrivate will NOT be added to the include directory search path for
> > 
> 
> > > > the compilation of bar.c of mylib.
> > 
> 
> > > >
> > 
> 

> > > The example is illustrative (transitivity - PRIVATE is not propagated)
> > 
> 

> > > > This is a very short summary, but I hope it is of help to you. There
> > 
> 
> > > > are other ressources on the Internet. E. g.
> > 
> 
> > > > *
> > 
> 
> > > > https://stackoverflow.com/questions/26037954/cmake-target-link-libraries-interface-dependencies
> > 
> 
> > > > * https://rix0r.nl/blog/2015/08/13/cmake-guide/
> > 
> 
> > > >
> > 
> 
> > > > Regards,
> > 
> 
> > > > Rainer
> > 
> 
> > > >
> > 
> 
> > > --
> > 
> 

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> --
> Eric
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