[CMake] How to add dependency relations between libs and executable

[vakano]

Hi, Chuck,

Thanks for your great help! "Lib_B and Lib_C, build before A" that is
exactly what I need.

So for this parallel project structure, an upper level cmakelist used to
organize and setup 

relationship with lib A, B, C right?

One more question is, if use the upper level cmake list, lib_B , lib_C can
be invoked directly 

without import in proj_a?

Thanks,
Le


Chuck Atkins wrote
>> cmake, the old top layer project is proj_a, which at the same layer with
>> proj_b and proj_c, if I add an extra top layer as the root you mentioned,
> 
> the generated make file structure will be changed, top layer make file
> 
> will be root instead of proj_a.
>>
>> Is there any way to add the dependency at proj_a level?
>>
> 
> If you want proj_a, proj_b, and proj_c to all be built by the same make
> command, then it makes sense to have a top level organization that
> encompasses them all.  Also, if proj_a, proj_b and proj_c don't make sense
> on their own and only when paired with each-other, then I would take the
> "project(...)" command out of each of them and only leave the top level.
> Basically, anything that has a project(...) command can be configured and
> built all on it's own without the rest of the tree.  In this case, it may
> make sense to keep b and c as independent projects but a as not since it
> needs b and c.  So for example, similar to Anatoly's example:
> 
> *folder*
> CMakeLists.txt:
> project(root)
> add_subdirectory(proj_b)
> add_subdirectory(proj_c)
> add_subdirectory(proj_a)
> 
> *folder/proj_a*
> CMakeLists.txt:
> add_executable(*A *main.cpp)
> target_link_libraries(*A B C*)
> 
> *folder/proj_b*
> CMakeLists.txt:
> project(proj_b)
> add_library(B proj_b.cpp)
> 
> *folder/proj_c*
> CMakeLists.txt:
> project(proj_c)
> add_library(*C *proj_c.cpp)
> 
> 
> With this structure, you can configure and build just project b or c:
> 
> $ mkdir build_c
> $ cd build_c
> $ cmake /path/to/folder/proj_c
> ...
> $ make
> ...
> 
> You end up with libC.a .  Similarly, you could do that for proj_b and get
> libB.a.  Or, if you configure the top level project instead:
> 
> $ mkdir build_all
> $ cd build_all
> $ cmake /path/to/folder
> ...
> $ make
> Scanning dependencies of target B
> [ 16%] Building CXX object proj_b/CMakeFiles/B.dir/proj_b.o
> [ 33%] Linking CXX static library libB.a
> [ 33%] Built target B
> Scanning dependencies of target C
> [ 50%] Building CXX object proj_c/CMakeFiles/C.dir/proj_c.o
> [ 66%] Linking CXX static library libC.a
> [ 66%] Built target C
> Scanning dependencies of target A
> [ 83%] Building CXX object proj_a/CMakeFiles/A.dir/main.o
> [100%] Linking CXX executable A
> [100%] Built target A
> $
> 
> You end up with proj_b/libB.a, proj_c/libC.a, and proj_a/A which is linked
> with libB.a and libC.a.  You can also do a parallel make with make
> -j(whatever) adn the generated dependencies will make sure that targets
> and
> individual files are built in the right order.  Technically speaking, you
> don't *need* to have a CMakeLists.txt at each level and you could put it
> all in to one top level CMakeLists.txt but it's generally considered poor
> CMake code to do so.  A good rule of thumb is to have a CMakeLsits.txt
> file
> at each level that a target (i.e. a library or executable) is built and a
> top level CMakeLists.txt to tie it all together.  This is the same sort of
> approach you see with autoconf where it's typical to have a Makefile.am at
> each level.
> 
> -- 
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