[CMake] Absolute Path linking library

[Clinton Stimpson]

On Wednesday, September 04, 2013 11:30:51 AM Laurent Chauvin 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) ?

For Linux, the rpath feature for shared libraries already works well, but it 
appears you are actually making static library on Linux.  For Mac, the 
equivalent of that Linux/Unix rpath feature was added to CMake 2.8.12.

For Windows, if there is a DLL, users of a dll commonly edit their PATH 
environment variable to help find it at runtime.  There really isn't anything 
you as the author of the dll can do to help that.

> 
> 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 ?

Yes, there is a better way.  Use install(EXPORT ..), which will take care of 
those details for you.

Your MyLibConfig.cmake/mylib-config.cmake file can include it.

Clint


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