[CMake] Location of library to be linked changing over time

[Bill O'Hara]

Thanks - I wasn't sure I was explaining very clearly! I think "retriggering
find_library" is a far more concise way to say it.

Could perhaps a cmake developer comment on whether its possible to do this?
Is there some workaround we could currently use to retrigger the
find_library to check whether we need to relink before running an executable
via a make target?


2009/4/30 Adolfo Rodríguez <dofo79 at gmail.com>

> I understand perfectly what you say, but it doesn't look like it's the
> currently implemented policy for retriggering find_library. Right now it
> looks like it all depends on the value of the cached variable. I have a
> somewhat similar use-case where I want to force find_package to look again
> for a package, but my current solution has to be triggered by the user (but
> we're OK with that).
>
> Cheers
>
> 2009/4/30 Bill O'Hara <billtohara at gmail.com>
>
> Apologies - meant to hit reply all.
>>
>>
>> ---------- Forwarded message ----------
>> From: Bill O'Hara <billtohara at gmail.com>
>> Date: 2009/4/30
>> Subject: Re: [CMake] Location of library to be linked changing over time
>> To: Adolfo Rodríguez <dofo79 at gmail.com>
>>
>>
>> Hi Adolfo,
>>
>> Thanks for the suggestion. I understand that I can rerun cmake and have it
>> find the new library version - perhaps even just a make rebuild_cache before
>> each make test would work.
>>
>> However, what I really would like to do is not have to do that *manually*.
>> Our users have libraries in one of two places, "a" and "b". If a library
>> exists in "a" it should always be used even if we have previously linked
>> against a version in "b". So I need to find some way to track dependencies
>> between a user of a library and the library, and trigger a relink if a new
>> version of a library has appeared in one of those locations with "a" always
>> winning if a library is in both places.
>>
>> Let me rephrase the problem. I can add link_directories for "a" and "b"
>> and have a build work by searching for libraries in those places at build
>> time via -L flags to the compiler (not at cmake config time). But, that
>> means cmake can't track dependencies because it doesn't know which file path
>> we'll end up really linking with in the end.
>>
>> Does that make sense?
>> Thanks
>> b.
>>
>>
>> 2009/4/30 Adolfo Rodríguez <dofo79 at gmail.com>
>>
>> Hi Bill,
>>>
>>> When you invoke find_library, FOO is created as a cache entry. As long as
>>> FOO has a value (i.e., not FOO_NOTFOUND) find_library will not refresh its
>>> contents on succesive runs of cmake. If you unset(FOO CACHE) and rerun
>>> cmake, then the foo library will be searched for again.
>>> Is this a good enough solution for your situation?
>>>
>>> Regards,
>>>
>>> Adolfo
>>>
>>> On Thu, Apr 30, 2009 at 9:55 PM, Bill O'Hara <billtohara at gmail.com>wrote:
>>>
>>>> Lets say I have a CMakeLists.txt that looks like this
>>>>
>>>> find_library(FOO foo /tmp/a /tmp/b)
>>>> add_executable(bar bar.c)
>>>> target_link_libraries(bar ${FOO})
>>>> add_test(test_bar bar)
>>>>
>>>> then I run cmake, FOO is filled in with the located library from /tmp/b,
>>>> and I run make all;make test. All is good. If I change /tmp/b/libfoo.a then
>>>> when I run make test the executable is relinked before I execute it. All is
>>>> good again.
>>>>
>>>> Now lets say a newer copy of the library appears in /tmp/a.
>>>>
>>>> When I run make test, what I'd like to happen is that we notice it has
>>>> appeared, and relink against it because we prefer to use /tmp/a/libfoo.a if
>>>> it exists (hence the order in the find_library).
>>>>
>>>> Is there a way to make that happen? I think if I wrote a raw makefile I
>>>> could do this with vpaths or somesuch and still get the dependency checking
>>>> ok. Is there a way with cmake?
>>>>
>>>> Thanks
>>>> b.
>>>>
>>>>
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>>>
>>>
>>>
>>> --
>>> Adolfo Rodríguez Tsouroukdissian
>>>
>>> Robotics engineer
>>> PAL ROBOTICS S.L
>>> http://www.pal-robotics.com
>>> Tel. +34.93.414.53.47
>>> Fax.+34.93.209.11.09
>>>
>>
>>
>>
>
>
> --
> Adolfo Rodríguez Tsouroukdissian
>
> Robotics engineer
> PAL ROBOTICS S.L
> http://www.pal-robotics.com
> Tel. +34.93.414.53.47
> Fax.+34.93.209.11.09
>
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