[CMake] Problem with LINK_DIRECTORIES

[Clinton Stimpson]

That's what I do sometimes.  To make that easier, CMake gives some convenience 
variables for library prefixes and suffixes if you are on multiple platforms.

Clint

On Monday, November 14, 2011 01:20:29 pm David Cole wrote:
> If you already know where all the libraries are, please just use the
> full paths to those libraries, and do not use find_library.
> 
> On Mon, Nov 14, 2011 at 3:15 PM, Robert Dailey <rcdailey at gmail.com> wrote:
> > On Mon, Nov 14, 2011 at 1:59 PM, Michael Hertling <mhertling at online.de>
> > 
> > wrote:
> >> On 11/14/2011 06:17 PM, Robert Dailey wrote:
> >> > Well maybe you can tell me I'm doing this wrong then, but based on how
> >> >I
> >> >
> >> > am
> >> > currently setting up my third party libraries, it is required.
> >> > 
> >> > So basically all third party libraries we use are not installed
> >> > individually, instead we have a server on our intranet that contains
> >> > precompiled versions of all libraries in a specific and consistent
> >> > hierarchy. For this reason, it doesn't make sense to use
> >> > find_library(), which would normally always give you absolute paths
> >> > to your library files
> >> > and thus link_directories() would not be needed.
> >> > 
> >> > Instead I have a script in CMake that iterates each third party
> >> > library and
> >> > adds its lib link directory to a list. When done I take this whole
> >> > list of
> >> > link directories and pass it to link_directories() in my top level
> >> > CMakeLists file, this way each and every project will include all of
> >> > the third party library lib directories to have access to them.
> >> 
> >> Instead of populating a list with the libraries' directories, you might
> >> set up one variable for each library containing the latter's full path,
> >> e.g. ZLIB_LIBRARY or BDB47_LIBRARY. Since you do this in the top-level
> >> CMakeLists.txt, these variables propagate to subordinate CMakeLists.txt
> >> files and, thus, will be known wherever they are needed in your project.
> >> 
> >> > For each target I simply create a list of my libs, like so:
> >> > 
> >> > set( libraries zlib libbdb47 )
> >> 
> >> SET(libraries ${ZLIB_LIBRARY} ${BDB47_LIBRARY})
> >> 
> >> > I pass each one of these to target_link_libraries() and I leave it up
> >> > to the compiler to search for where to find the file in the provided
> >> > link directories.
> >> 
> >> An unrestricted use of LINK_DIRECTORIES() means asking for trouble;
> >> especially with numerous directories, there's a growing probability
> >> that the -L option will lure the linker into a wrong directory some
> >> day. There're even situations which can't be resolved with -L/-l at
> >> all: Suppose you have a directory x with liba.so and libb.so, and a
> >> directory y with different versions of lib{a,b}.so. Suppose further
> >> you want to link against x/liba.so and y/libb.so. How do you achieve
> >> this with LINK_DIRECTORIES() and TARGET_LINK_LIBRARIES()? Reversely,
> >> insisting on the use of LINK_DIRECTORIES() limits the possibilities
> >> how to organize the libraries on your intranet server. IMO, these
> >> are actual drawbacks. OTOH, you must know the libaries' locations
> >> to use LINK_DIRECTORIES(), and the libraries must be known anyway,
> >> so why not join the locations to the libraries and use full paths?
> > 
> > Problem is, if I end up using find_library(), I will have to provide hint
> > search directories for each and every single library, and there are about
> > 20 of them. This to me is the same as just generating a list of
> > directories and including those directly, and a lot less trouble.
> > find_library() is great and I really wanted to use it for this, but to me
> > the benefits of using it diminish when we are not using third party
> > libraries installed in a non deterministic location. If a user installs
> > the third party libraries in different locations on each of their
> > machines, and different versions, it makes more sense to use it in that
> > case.
> > Why should I let CMake search & find a library when I already know where
> > it is? Simply to get absolute paths to those libraries? If I want
> > absolute paths I can think of much better ways to do
> > it, preferably through string concatenation.
> > Another issue is that 80% of the libraries we use do not have a
> > pre-packaged Find module provided by CMake. This means I'd end up
> > writing 80% of the find modules myself. This is a lot of work for no
> > perceived benefit.
> > With my points made and circumstances explained, can you still give me a
> > good reason to use find_library?
> > I understand and agree with the issues that come with using
> > link_directories(), however I haven't run into those issues yet and our
> > consistent organization of third party libraries on our intranet server
> > are carry over from our legacy build system that I'm replacing.
> > --
> > 
> > Powered by www.kitware.com
> > 
> > Visit other Kitware open-source projects at
> > http://www.kitware.com/opensource/opensource.html
> > 
> > Please keep messages on-topic and check the CMake FAQ at:
> > http://www.cmake.org/Wiki/CMake_FAQ
> > 
> > Follow this link to subscribe/unsubscribe:
> > http://www.cmake.org/mailman/listinfo/cmake
> 
> --
> 
> Powered by www.kitware.com
> 
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
> 
> Please keep messages on-topic and check the CMake FAQ at:
> http://www.cmake.org/Wiki/CMake_FAQ
> 
> Follow this link to subscribe/unsubscribe:
> http://www.cmake.org/mailman/listinfo/cmake

-- 
Clinton Stimpson
Elemental Technologies, Inc
Computational Simulation Software, LLC
www.csimsoft.com