[CMake] add_subdirectory and build directory

Marcel Loose loose at astron.nl
Tue Sep 15 07:27:42 EDT 2009 

Aah, I see now what the problem really is.

You're building in two different directories. So, you will end up with
two versions of libMaths. That exactly explains the output you're
seeing.

* First, in directory Maths, you're building libMaths.
* Next, in directory HelloMath, you're building both HelloMath and
libMaths, the latter due to the link dependency. The library libmMaths
is not up-to-date as you suggest; it hasn't been built yet!
* Finally, in directory Math, you're building libMaths again, but now
it's up-to-date, so nothing needs to be done.

Best regards,
Marcel Loose.

On Tue, 2009-09-15 at 10:16 +0200, Pierre-Julien Villoud wrote:
> I found my problem
> 
> Here are 2 CMakeLists.txt : 
> 
> ===================================
> CMakeLists.txt : libMaths : 
> 
> #Minimum Cmake version required
> cmake_minimum_required(VERSION 2.6)
> 
> add_library(Maths
> 	MathFuncsLib.cpp
> )
> ===================================
> 
> ===================================
> CMakeLists.txt : HelloMath : 
> 
> #Minimum Cmake version required
> cmake_minimum_required(VERSION 2.6)
> 
> include_directories(../Math)
> 
> link_directories(../Math)
> 
> add_executable(HelloMath
> 	hellomath.cpp
> )
> 
> target_link_libraries(HelloMath
> 	Maths
> )	
> 
> add_subdirectory(../Math ../Math)
> ===================================
> 
> My build process is the following : 
> Cmake (...) && make
> 
> And it's the cmake call that causes the problem : 
> 
> In C:\Maths : 
> > Cmake -G"MinGW Makefiles" -DCMAKE_BUILD_TYPE=Release && make => builds libMaths
> 
> In C:\HelloMath : 
> > Cmake -G"MinGW Makefiles" -DCMAKE_BUILD_TYPE=Release && make => builds HelloMath AND builds libMaths (whereas it's up to date) because of the cmake call.
> 
> The following works : 
> In C:\HelloMath : 
> > Cmake -G"MinGW Makefiles" -DCMAKE_BUILD_TYPE=Release && make => builds HelloMath AND builds libMaths because of the cmake call.
> 
> In C:\Maths : 
> > make => does not build libMaths since it's up to date.
> 
> So I must try to remove the cmake call and it will be fine !
> 
> Sorry to have bothered you...
> 
> Thanks !
> 
> Pierre-Julien VILLOUD
> 
> -----Message d'origine-----
> De : Marcel Loose [mailto:loose at astron.nl] 
> Envoyé : mardi 15 septembre 2009 09:38
> À : Pierre-Julien Villoud
> Cc : cmake at cmake.org
> Objet : RE: [CMake] add_subdirectory and build directory
> 
> Hi Pierre-Julien,
> 
> You are right. You don't need add_dependencies() when specifying link
> dependencies using target_link_libraries(). The latter, BTW, is of
> course the preferred way to do this.
> 
> Without an example of you CMakeLists.txt files, it's very hard to tell
> what, if anything, is going wrong.
> 
> Regards,
> Marcel Loose.
> 
> On Mon, 2009-09-14 at 16:28 +0200, Pierre-Julien Villoud wrote:
> > Sorry I did not reply to you...
> > 
> > I actually use the target_link_libraries and the add_dependencies which is useless if using the target_link_libraries (I think ?)
> > 
> > So I really wonder why my objects are re-built... It's still a mystery for me !
> > 
> > Thanks again
> > 
> > Pierre-Julien VILLOUD
> > 
> > -----Message d'origine-----
> > De : Marcel Loose [mailto:loose at astron.nl] 
> > Envoyé : vendredi 11 septembre 2009 18:09
> > À : Pierre-Julien Villoud
> > Cc : cmake at cmake.org
> > Objet : Re: [CMake] add_subdirectory and build directory
> > 
> > Hi Pierre-Julien,
> > 
> > I think I see what the problem is. You didn't specify any dependencies.
> > You mention that project A depends on B. But don't you actually mean
> > that libA depends on libB? If that's the case you should add a
> > target_link_libraries(libA libB) to the CMakeLists.txt file of project
> > A.
> > 
> > Anyway, you may want to post your CMakeLists.txt files, so that people
> > can spot what you might be doing wrong. At the moment, I can only make
> > some wild guesses.
> > 
> > Best regards,
> > Marcel Loose.
> > 
> > On Fri, 2009-09-11 at 17:34 +0200, Pierre-Julien Villoud wrote:
> > > Hi and thanks for your answer...
> > > 
> > > Here is the ouput : 
> > > 
> > > I'm building A : My CMakelists.txt is in C:/A
> > > 
> > > -- Configuring done
> > > -- Generating done
> > > -- Build files have been written to: C:/A/Debug
> > > ==============Building A==============
> > > [  0%] Built target CMake
> > > Scanning dependencies of target B
> > > [  4%] Building CXX object C:/B/CMakeFiles/B.dir/B.cpp.obj
> > > Linking CXX static library C:\lib\libB.a
> > > [  4%] Built target B
> > > Linking CXX shared module C:\bin\A.dll
> > > [100%] Built target A
> > > 
> > > Then I'm building B : My CMakeLists.txt is in C:/B
> > > 
> > > -- Configuring done
> > > -- Generating done
> > > -- Build files have been written to: C:/B/Debug
> > > ==============Building B==============
> > > [  0%] Built target CMake
> > > Scanning dependencies of target B
> > > [100%] Building CXX object CMakeFiles/B.dir/B.cpp.obj
> > > Linking CXX static library C:\lib\libB.a
> > > [100%] Built target B
> > > 
> > > 
> > > Any clues ?
> > > 
> > > @Michael : I did not look at your long and precise answer (thank you very much for it BTW) but it seems quite complicated !! How are you managing your dependencies ?
> > > 
> > > Thank you for your help !
> > > 
> > > 
> > > 
> > > -----Message d'origine-----
> > > De : Marcel Loose [mailto:loose at astron.nl] 
> > > Envoyé : vendredi 11 septembre 2009 16:30
> > > À : Pierre-Julien Villoud
> > > Cc : cmake at cmake.org
> > > Objet : Re: [CMake] add_subdirectory and build directory
> > > 
> > > Hi Pierre-Julien,
> > > 
> > > Are you sure it's rebuilding? CMake (or 'make' actually), prints a lot
> > > of messages "Built target ..." even if no compilation was needed.
> > > However, if you also see messages like "Building ..." then it is
> > > actually rebuilding.
> > > 
> > > Without an example of the output of your build, it is hard to judge
> > > what, if anything, is going wrong.
> > > 
> > > Best regards,
> > > Marcel Loose.
> > > 
> > > On Fri, 2009-09-11 at 15:12 +0200, Pierre-Julien Villoud wrote:
> > > > Hi everyone, 
> > > > 
> > > >  
> > > > 
> > > > After unsuccessfully looking for an answer on Google, I contact you.
> > > > 
> > > > I have a question regarding the use of add_subdirectory. When a
> > > > project A is depending on a project B, I add the following in A's
> > > > CMakeLists.txt : 
> > > > 
> > > >  
> > > > 
> > > > Add_subdirectory(B Path/To/B/Build/Directory)
> > > > 
> > > >  
> > > > 
> > > > It does build B before A. But when I build B in its build directory
> > > > and I build A after, it builds B again whereas it should not since B
> > > > is up to date.
> > > > 
> > > >  
> > > > 
> > > > Anyone sees what's wrong ?
> > > > 
> > > >  
> > > > 
> > > > Thanks in advance
> > > > 
> > > >  
> > > > 
> > > > Pierre-Julien VILLOUD
> > > > 
> > > > 
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