[CMake] Dependent Libraries added automatically?

[Bill Hoffman]

Mike Jackson wrote:
> I started noticing some warnings when I am linking my project 
> executables that bascially says libraries are listed multiple times on 
> the link line. Now this is just a warning so I _could_ ignore it but I 
> am curios about how cmake is working at this point. Here is what I have:
> 
> Library MXADataModel built by CMake.
> It depends on Expat, Tiff and HDF5 (which are installed on the local 
> filesystem and NOT build by cmake).
> 
> I have some Examples that are built in the same project as the 
> MXADataModel library. Lets take one of those examples as and "example"..
> 
> SET (DATAIMPORT_EXAMPLE_SOURCES
> ${MXA_SOURCE_DIR}/src/Examples/DataImport/main.cpp
> ${MXA_SOURCE_DIR}/src/Examples/DataImport/SimpleImportExample.cpp
> ${MXA_SOURCE_DIR}/src/Examples/DataImport/ExampleImportDelegate.cpp
> ${MXA_SOURCE_DIR}/src/Examples/DataImport/ExampleImportDelegateFactory.cpp
> )
> SET (DATAIMPORT_EXAMPLE_HEADERS
>   ${MXA_SOURCE_DIR}/src/Examples/DataImport/SimpleImportExample.h
>   ${MXA_SOURCE_DIR}/src/Examples/DataImport/ExampleImportDelegate.h
>   ${MXA_SOURCE_DIR}/src/Examples/DataImport/ExampleImportDelegateFactory.h
> )
> source_group(src\\Examples\\DataImport FILES 
> ${DATAIMPORT_EXAMPLE_SOURCES} ${DATAIMPORT_EXAMPLE_HEADERS})
> ADD_EXECUTABLE(DataImportExample ${DATAIMPORT_EXAMPLE_SOURCES})
> TARGET_LINK_LIBRARIES(DataImportExample ${MXADATAMODEL_LIB_NAME} )
> 
> 
> 
> MXADATAMODEL_LIB_NAME is the name of the MXADataModel library that is 
> built earlier in the project and has dependencies on hdf5, tiff and expat.
> 
> If I use the code as is then cmake will actually add the tiff, hdf5 and 
> expat libraries to the link line. Is CMake _supposed_ to do that? This 
> is building shared libraries and tiff, expat and hdf5 are all dylibs 
> also. Building MXADataModel as a static library shows the same behavior.
> 
>  This is on OS X 10.5.5 with Xcode 3.1.x tooling generating Makefiles. 
> Same thing using Xcode generated targets. So maybe I just don't 
> understand how linking works on OS X?
> 
> Just wondering if I make changes to the CMake files will it mess up 
> windows builds?
> 
Yes, cmake automatically chains this stuff.

add_library(a ...)
target_link_library(a b c)

add_executable(foo ...)
target_link_libraries(foo a)

This will cause foo to link to a b c.

With CMake 2.6.2 you can stop this from happening with a target property:

http://www.cmake.org/cmake/help/cmake2.6docs.html#prop_tgt:LINK_INTERFACE_LIBRARIES

-Bill