[CMake] Problem with LINK_DIRECTORIES

Mon Nov 14 16:38:46 EST 2011

From the Modules/Platform/* files, it looks like the only difference between the 
two is when using CYGWIN or MinGW.  I'm not sure which to use.

Clint

On Monday, November 14, 2011 01:51:49 pm Robert Dailey wrote:
> What is the difference between CMAKE_LINK_LIBRARY_SUFFIX and
> CMAKE_IMPORT_LIBRARY_SUFFIX? Which should I use?
> 
> ---------
> Robert Dailey
> 
> On Mon, Nov 14, 2011 at 2:49 PM, Clinton Stimpson 
<clinton at elemtech.com>wrote:
> > 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

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