On 2010-04-20 03:27, Michael Hertling wrote:
On 04/19/2010 10:07 PM, Benoit Thomas wrote:
I'm using an external library which is already compiled. I have wrapped
the library in a MyLib.cmake and use it in cmake as an imported library.
It works fine, but since the include line uses relative path, it changes
from projects to projects and in some case it looks just wrong.
Just for my understanding: What exactly do you mean with "wrapped the
library in a MyLib.cmake" and "use it in cmake as an imported library"?
I'm migrating Visual Studio project to CMake. The Visual Studio projects
use heavy configurations (20+). So, when I used a library which hasn't
yet been converted to cmake, I usually only create a small
CMakeLists.txt for it which look like this:
add_library (MyLib IMPORTED)
set_target_properties (MyLib PROPERTIES IMPORTED_LOCATION_CONFIG1
"${MYLIB_ROOT_DIR}/bin/config1/MyLib.lib")
set_target_properties (MyLib PROPERTIES IMPORTED_LOCATION_CONFIG2
"${MYLIB_ROOT_DIR}/bin/config2/MyLib.lib")
...
set_target_properties (MyLib PROPERTIES IMPORTED_LOCATION_CONFIG20
"${MYLIB_ROOT_DIR}/bin/config20/MyLib.lib")
Then, in another project I'm doing (something like):
include (../../../somewhere/MyLib/CMakeLists.txt)
add_executable (MyExe)
target_link_libraries (MyExe MyLib)
But this line didn't feel right:
include (../../../somewhere/MyLib/CMakeLists.txt)
I renamed the CMakeLists.txt to MyLib.cmake as it's not really a project
file on his own. Also, the path is never the same for all projects so
that's why I wanted to change the format to a find_package (it's
cleaner, and doesn't change if projects are moved).
I want to change this to something more like:
find_package (MyLib)
include (MYLIB_CMAKE_FILE)
# add_executable and stuff
target_link_libraries (MyExe MyLib)
This is a possible approach which is also followed by FindQt4.cmake,
but, for several reasons, you shouldn't explicitly refer to "MyLib"
in TARGET_LINK_LIBRARIES(); use variables from FIND_PACKAGE(MyLib).
I though about using variables, but target_link_libraries doesn't
support configurations, and the other alternative I found was using
LINK_FLAGS. However, using imported library and target_link_libraries
gave me a clean solution.
In the book, there is an example which seems to do more what I want and
use *-config.cmake, which give something like
find_package (MyLib)
# no include, since the MyLib-config.cmake already took care of the include
# add_executable and stuff
target_link_libraries (MyExe MyLib)
What is meant with "took care of the include"? I don't have the book. ;)
When I look at FindXXX.cmake, they create variables and macros, but they
don't add any targets to your project (I assume this was standard). In
the book, there's an example about creating XXX-config.cmake files. From
my understanding, the XXX-config.cmake include a XXX-targets.cmake which
create the imported target.
So I was a little confuse about the fact that if I write code like
find_package (MyLib)
# If MyLib is a FindMyLib.cmake, the following code should like
if (MyLib_FOUND)
include (MyLib_USE_FILE) # which would do the add_library (MyLib
IMPORTED)
else()
# print some fatal error message...
endif()
# But if MyLib is a MyLib-config.cmake, there's nothing else to do;
find_package will display an error message if MyLib isn't found, and if
it's found, MyLib-config.cmake will include MyLib-target.cmake
Part of what I don't understand is when a user use the find_package
command, is he expecting to load a Find* file or a *-config file (or he
doesn't care?), [...]
In general, he doesn't care; in particular, she can tell
FIND_PACKAGE() to look for a config file exclusively.
The more I'm reading about the subject, the more I'll go with a
XXX-config.cmake file which will take care of importing the library. And
as you mention, I'll try to use variables as much as possible, but in my
context is a little hard :) I'll also use the NO_MODULE option to make
it clear I'm looking for a config file and not a module.
As for myself: Yes, absolutely. FIND_PACKAGE(MyLib) should try to find
anything necessary to use Mylib, i.e. preprocessor definitions, include
directories, libraries etc., and communicate the results as variables,
e.g. MyLib_DEFINITIONS, MyLib_INCLUDE_DIRS, MyLib_LIBRARIES etc., but it
should not have a direct, hard-coded impact on the configuration process
as a target definition would be; this should be reserved for the calling
CMake script. BTW, why would you need a target "MyLib" here? As you said
before, the library is external and already compiled.
The reason why I need a MyLib target is because of the 20+
configurations... Make my life more easy that way (Keeping the 20+
configurations in a single project is not really my call btw...)
'hope this helps a little bit, and to CMake experts: Feel free to beat
me if I'm telling nonsense, but give some enlightenment afterward. ;-)
Yeah, it helped a lot, thank you very much !!!
Ben.
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