[CMake] Absolute Path linking library

Clinton Stimpson clinton at elemtech.com
Wed Sep 4 13:18:41 EDT 2013 

On Wednesday, September 04, 2013 12:48:41 PM Laurent Chauvin wrote:
> Yes I'm using 2.8.12-rc2 for the library and the example.
> 
> But my example is not in the same directory as my library.

Neither was my example.

> 
> I can see in your example you specify the full path in
> target_link_libraries of your library, which I could probably do.
> 
> The problem is, if later on my library I want to put the .dyld not in
> MyLib/lib but MyLib/testLib, then I will have (or users) to modify all
> their CMakeLists to modify path of the library.
> That's why I would like not to have to hardcode the library path into my
> example.

Of course the users shouldn't hard code it.  My example was simply 
demonstrating the solution to the problem of locating the shared library at 
runtime, which works in 2.8.12-rc2, without setting DYLD_LIBRARY_PATH.

Really, this problem/solution for finding the .dylib at runtime has nothing to 
do with whether your target_link_libraries() has a full path or not.  Or 
whether you are using LINK_DIRECTORIES or not.
I just tested with full path vs. LINK_DIRECTORIES, and it makes no difference 
to whether the library can be found at runtime.

As an aside, I'm encouraging you to not use LINK_DIRECTORIES.

Clint

> 
> I'm using find_package to find my library, and include the use file, which
> define the include_directories and link_directories.
> 
> I also checked the INSTALL(EXPORT ..), here
> http://www.cmake.org/Wiki/CMake/Tutorials/How_to_create_a_ProjectConfig.cmak
> e_file but I don't understand what it's doing and how it works.
> 
> Thank you.
> -Laurent
> 
> On Wed, Sep 4, 2013 at 12:26 PM, Clinton Stimpson 
<clinton at elemtech.com>wrote:
> > On Wednesday, September 04, 2013 12:02:55 PM Laurent Chauvin wrote:
> > > Thank you for you help Clint.
> > > 
> > > I actually relinked, but as you said I still had the LINK_DIRECTORIES.
> > > However, if I remove it, I have a linking error telling me it cannot
> > > find
> > > the library.
> > > 
> > > Should I keep the library in Target_Link_Libraries, or with new flags,
> > > dependency will automatically find the library ?
> > 
> > You can leave your LINK_DIRECTORIES as its not the cause of your runtime
> > failure to find the library.
> > 
> > For compiling MyExample, did you also use CMake 2.8.12 RC?
> > 
> > Here's a minimal example that works for me.
> > 
> > -- lib/CMakeLists.txt
> > set(CMAKE_MACOSX_RPATH 1)
> > add_library(lib SHARED lib.cpp)
> > 
> > -- app/CMakeLists.txt
> > add_executable(app app.cpp)
> > target_link_libraries(app ${CMAKE_CURRENT_LIST_DIR}/../lib/liblib.dylib)
> > 
> > In lib/
> > I run "cmake . && make"
> > 
> > In app/
> > I run "cmake . && make && ./app"
> > 
> > With 2.8.12, it works.
> > 
> > With an older version, I get
> > dyld: Library not loaded: @rpath/liblib.dylib
> > 
> >   Referenced from: ..../app
> >   Reason: image not found
> > 
> > Trace/BPT trap
> > 
> > Clint
> > 
> > > Thank you.
> > > -Laurent
> > > 
> > > On Wed, Sep 4, 2013 at 11:59 AM, Clinton Stimpson
> > 
> > <clinton at elemtech.com>wrote:
> > > > On Wednesday, September 04, 2013 11:53:45 AM Laurent Chauvin wrote:
> > > > > Hello,
> > > > > 
> > > > > I just tried to set the MACOSX_RPATH 1 in the top CMakeLists of
> > 
> > MyLib,
> > 
> > > > and
> > > > 
> > > > > when I now do otool -L libMyLib.dyld, I can indeed see
> > > > 
> > > > @rpath/libMyLib.dyld.
> > > > 
> > > > > However, my executable "MyExample" is still not able to find the
> > 
> > library
> > 
> > > > at
> > > > 
> > > > > runtime. When I do otool -L MyExample, I still have libMyLib.dyld,
> > 
> > not
> > 
> > > > > @rpath/libMyLib.dyld.
> > > > 
> > > > Did you relink MyExamle against the new libMyLib.dylib?  CMake doesn't
> > > > modify
> > > > the install names of libraries being linked against, so if otool -L
> > > > MyExample
> > > > still gives "libMyLib.dylib", I'm assuming you didn't relink it.
> >  
> >  Using a
> >  
> > > > cmake generated export file would take care of setting up dependencies
> > 
> > so
> > 
> > > > the
> > > > relink would happen simply by doing a make.  If you use
> > 
> > LINK_DIRECTORIES,
> > 
> > > > you
> > > > miss the relink dependency.
> > > > 
> > > > Clint
> > > > 
> > > > > And I have same error (Library not loaded, image not found) when
> > 
> > trying
> > 
> > > > to
> > > > 
> > > > > start the example.
> > > > > 
> > > > > Should I add something more (or remove something) from my CMakeLists
> > > > > example ?
> > > > > 
> > > > > I'm sorry I'm not really familiar with these mechanisms.
> > > > > 
> > > > > Thank you very much.
> > > > > -Laurent
> > > > > 
> > > > > 
> > > > > On Wed, Sep 4, 2013 at 11:30 AM, Laurent Chauvin
> > > > > 
> > > > > <lchauvin at bwh.harvard.edu>wrote:
> > > > > > Thank you very much for your answer.
> > > > > > 
> > > > > > I will try to use the MACOSX_RPATH.
> > > > > > 
> > > > > > However, I have some questions. As the flag suggests, it's only
> > > > > > for
> > > > 
> > > > mac.
> > > > 
> > > > > > Is there anything similar for Linux (and eventually Windows
> > 
> > systems) ?
> > 
> > > > > > Also, the problem to set the full path of the library is, if I
> > 
> > compile
> > 
> > > > on
> > > > 
> > > > > > Windows the extension of library will be dll, on Mac it will be
> > 
> > dyld,
> > 
> > > > and
> > > > 
> > > > > > .a on linux.
> > > > > > I could make a condition to set the extension at the end of the
> > 
> > name
> > 
> > > > > > of
> > > > > > the library like libMyLib.(dll, dyld, a) but, I feel like it's not
> > > > 
> > > > really
> > > > 
> > > > > > a
> > > > > > clean way to do it.
> > > > > > 
> > > > > > Is there a better way to do it ?
> > > > > > 
> > > > > > Thank you very much.
> > > > > > -Laurent
> > > > > > 
> > > > > > On Wed, Sep 4, 2013 at 10:57 AM, Clinton Stimpson
> > > > 
> > > > <clinton at elemtech.com>wrote:
> > > > > >> On Tuesday, September 03, 2013 09:47:45 PM Laurent Chauvin wrote:
> > > > > >> > Hello everyone,
> > > > > >> > 
> > > > > >> > I'm working on a library, and I would like the users be able to
> > > > 
> > > > create
> > > > 
> > > > > >> their
> > > > > >> 
> > > > > >> > own program and liking to my library (by specifying path in
> > 
> > cmake).
> > 
> > > > > >> > I created the library and an example to test it.
> > > > > >> > Everything compiles.
> > > > > >> > 
> > > > > >> > However, when I try to run my example I have this error:
> > > > > >> > 
> > > > > >> > MyExample:
> > > > > >> >       libMyLib.1.dylib (compatibility version 1.0.0, current
> > > > > >> >       version
> > > > > >> 
> > > > > >> 1.0.0)
> > > > > >> 
> > > > > >> >       /usr/lib/libstdc++.6.dylib (compatibility version 7.0.0,
> > > > 
> > > > current
> > > > 
> > > > > >> version
> > > > > >> 
> > > > > >> > 56.0.0) /usr/lib/libSystem.B.dylib (compatibility version
> > > > > >> > 1.0.0,
> > > > > >> > current
> > > > > >> > version 169.3.0)
> > > > > >> > 
> > > > > >> > The problem is my example is not in the same directory as my
> > > > > >> > library
> > > > > >> 
> > > > > >> (not
> > > > > >> 
> > > > > >> > even in a subdirectory). And it seems it's linking to my
> > > > > >> > library
> > > > 
> > > > with a
> > > > 
> > > > > >> > relative path.
> > > > > >> > 
> > > > > >> > If I add the path of my library in DYLD_LIBRARY_PATH it works,
> > 
> > but
> > 
> > > > > >> > I
> > > > > >> 
> > > > > >> would
> > > > > >> 
> > > > > >> > like the users to be able to compile and link straight forward.
> > > > > >> > 
> > > > > >> > To link the library to my example I use find_package(MyLib
> > > > > >> > REQUIRED)
> > > > > >> > and
> > > > > >> > include(${MyLib_USE_FILE}) which basically do a
> > > > > >> > LINK_DIRECTORIES
> > > > 
> > > > with
> > > > 
> > > > > >> the
> > > > > >> 
> > > > > >> > absolute path of the library.
> > > > > >> > 
> > > > > >> > Then I do add_executable and target_link_libraries(MyExample
> > > > > >> > ${MyLib_LIBRARIES})
> > > > > >> > 
> > > > > >> > Compilation is working fine. There is these options:
> > > > > >> > 
> > > > > >> > -L/Absolute/Path/To/MyLib -lMyLib
> > > > > >> > 
> > > > > >> > But at runtime, library cannot be found.
> > > > > >> > 
> > > > > >> > Would it be possible to put the full path of my library when
> > > > 
> > > > linking in
> > > > 
> > > > > >> the
> > > > > >> 
> > > > > >> > CMakeLists ?
> > > > > >> 
> > > > > >> You should use the full path to the library instead of
> > > > 
> > > > LINK_DIRECTORIES.
> > > > 
> > > > > >> Its easiest if you use install(EXPORT ...) to have CMake generate
> > 
> > an
> > 
> > > > > >> export
> > > > > >> file for you that can be included by your FindMyLib.cmake file.
> > > > > >> That export file will use the full path, and include any other
> > > > 
> > > > necessary
> > > > 
> > > > > >> information about the library.
> > > > > >> 
> > > > > >> But to solve the problem of finding the library at runtime
> > > > 
> > > > (specifying a
> > > > 
> > > > > >> full
> > > > > >> path won't solve it), CMake 2.8.12 has a new feature to address
> > > > 
> > > > exactly
> > > > 
> > > > > >> that
> > > > > >> problem.  For details: http://www.kitware.com/blog/home/post/510
> > > > > >> 
> > > > > >> If you can use CMake 2.8.12, then you need to put
> > > > > >> 
> > > > > >>  set(MACOSX_RPATH 1)
> > > > > >> 
> > > > > >> in the CMakeLists.txt of MyLib.
> > > > > >> 
> > > > > >> If the user is using 2.8.12, then any executable they compile
> > > > > >> with
> > > > 
> > > > your
> > > > 
> > > > > >> library will be able to find the library, no matter where it is.
> > > > > >> 
> > > > > >> By the way, 2.8.12 is in a release candidate stage right now, and
> > > > 
> > > > right
> > > > 
> > > > > >> now
> > > > > >> would be a good time for you to test the new feature that is
> > 
> > meant to
> > 
> > > > > >> solve
> > > > > >> your problem.
> > > > > >> 
> > > > > >> Clint
> > > > > > 
> > > > > > --
> > > > > > Laurent Chauvin, MS
> > > > > > Surgical Navigation and Robotics Laboratory, Radiology Department
> > > > > > Brigham And Women's Hospital, Harvard Medical School
> > > > > > http://wiki.ncigt.org/index.php/User:Lchauvin
> > > > 
> > > > --
-- 
Clinton Stimpson
Elemental Technologies, Inc
Computational Simulation Software, LLC
www.csimsoft.com

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