[CMake] Multiple calls to find_package(Boost) with different components

[Marcel Loose]

Hi Adolfo,

I think you already answered your question yourself, though maybe you
didn't realize it. Fortunately you wrote the key phrase

... Now if I clear all non-internal Boost_* cache variables ...

The thing is, FindBoost keeps track of the components it has already
found in internal variables named Boost_<component>_FOUND. So, if you
don't remove these variables from the cache, you're entering the realm
of undefined behaviour.

I don't know if the author(s) of FindBoost are to blame, e.g., for
possible abuse of internal variables; or that you should never do what
you did. I'm more of a command-line person, so I have no experience with
groups in the cmake-gui.

Best regards,
Marcel Loose.


On Mon, 2009-12-21 at 10:37 +0100, Adolfo Rodríguez Tsouroukdissian
wrote:
> Hi all,
> 
> I have a use case where find_package(Boost COMPONENTS xxx) is called
> more than once, and each time with a different set of components, as
> in the following example:
> 
> 
> cmake_minimum_required(VERSION 2.6)
> project(MyBoost)
> 
> find_package(Boost REQUIRED COMPONENTS date_time)
> message(STATUS "1st call: Boost_LIBRARIES=${Boost_LIBRARIES}")
> 
> find_package(Boost REQUIRED COMPONENTS regex)
> message(STATUS "2nd call: Boost_LIBRARIES=${Boost_LIBRARIES}")
> 
> 
> Upon configuring the project for the first time, everything works as
> expected, and the relevant output I get is:
> -- 1st call: Boost_LIBRARIES=/opt/boost/lib/libboost_date_time-mt.so
> -- 2nd call:
> Boost_LIBRARIES=/opt/boost/lib/libboost_date_time-mt.so;/opt/boost/lib/libboost_regex-mt.so
> 
> 
> Now if I clear all non-internal Boost_* cache variables, such as by
> removing the Boost group in cmake-gui and reconfigure my project, I
> get
> 
> -- 1st call: Boost_LIBRARIES=/opt/boost/lib/libboost_date_time-mt.so
> -- 2nd call: Boost_LIBRARIES=/opt/boost/lib/libboost_date_time-mt.so
> 
> 
> Which is unexpected. Should the above example work for the two
> described scenarios, or am I entering some state that yields undefined
> behavior?
> 
> Thanks in advance,
> 
> Adolfo
> 
> -- 
> Adolfo Rodríguez Tsouroukdissian, Ph. D.
> 
> 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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