[CMake] un circle dependency

[Alexander Neundorf]

On Thursday 11 November 2010, luxInteg wrote:
> Greetings
>
> I am learning cmake.
>
>   I think I now know how to generate libraries and executables but  I have
> not yet grasped  how  the tree and   directory structure is handled and by
> conseqence how one navigates therein.
>
>
> I have this problem.  Lets say my   build tree has these directories
>
> L---$originalSourceTree/build/lib
> M---$originalSourceTree/build/bin
>
> libraries   say libA.so libB.a are in L.  I want to generate   executables
> A.bin and B.bin in M but
> they each need  to link to  newly generated  libraries  libA.so libB.a
>
>
> a) how do I direct cmake  (in the CMakeLists.txt/base directory) to build 
> the libraries in ( L )above   first  -i.e. before atempting to do finds of
> nonexistant libraries  ?

The add_library() commands must be before the add_executable() commands, 
otherwise the libraries "A" and "B" are not yet know when you do 
target_link_libraries(exe A B)

Beside that, the dependencies in the generated makefiles are complete, so 
whenever you do a build, cmake makes sure that the libraries are up-to-date 
before it builds the executable.

> b) if I   insert lines such 'find_library(LIB  libA  path ../lib'   in the
> CmakeLists.txt in the base directory  this  results in an error  so what
> does one insert?

find_library() is not necessary, you can simply use the names of the library 
targets when linking against them.

> c) Further down the road, if the generated executables ae linked to 
> libraries in the build tree, what happens when one does a 'make install' to
> the 'permanent'  filesystem?  Are  the dependencies transfered?

No, not really.
You mean that the executables find the shared libs when starting ?
This depends on the loader. You can adjust this via the RPATH-related target 
properties.

Alex