[CMake] Absolute Path linking library

[Clinton Stimpson]

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