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

[Bill O'Hara]

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
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