[CMake] Absolute Path linking library

Clinton Stimpson clinton at elemtech.com
Wed Sep 4 12:26:59 EDT 2013 

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
> > 
> > --

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