[CMake] Howto to work with variables from central makefiles....

[Michael Hertling]

On 11/17/2010 04:56 PM, Thomas Lehmann wrote:
>>> for an automatically forced include I have provided an
>>>
>>> option like this:
>>>
>>>
>>>
>>> set(WIN32_SPEC
>> ${CMAKE_CURRENT_SOURCE_DIR}/../../libs/global/win32_spec.h)
>>
>> May you could use an absolute reference using
>>
>> ${PROJECT_SOURCE_DIR}/libs/global/win32_spec.h
>>
>> if your project is name TOTO
>> (from the PROJECT(TOTO CXX) statement)
>> you use
>>
>> ${TOTO_SOURCE_DIR}/libs/global/win32_spec.h.
> 
> it depends on how I use cmake. I can use the root of all
> sources or I use a subtree.
> Let's say I have following setup.
> 
> /src/libs
> /src/cmake
> /src/apps
> 
> when I call "cmake /src" or "cmake /src/apps" is relating the
> application to be build no difference but the variable CMAKE_SOURCE_DIR
> will change. My central files are in /src/cmake.
> 
> I would like avoiding to redefine search paths and variables in each individual
> makefile depending on its location in the source tree. One example:
> 
> <code>
> # ensuring that packages are found
> set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH}
>                       ${CMAKE_CURRENT_SOURCE_DIR}/../../scripts/make)
> 
> # most common definitions, macros, ... required by most projects
> find_package(AllOptions)
> </code>
> 
> I think that the problem is that cmake does not know where the real root
> is. I have not found something except adjusting an environment variable
> but this is something I would like to avoid when possible...

If you don't want to make /src the definite top-level directory of your
project(s) you must indeed provide a hint to /src/cmake since otherwise,
CMake cannot have an idea that there's additional stuff in this sibling,
e.g. "cmake -DCMAKE_CENTRAL_DIR=/src/cmake /src/apps". Alternatively,
you might always configure /src and use options to decide which
projects, i.e. subdirectories, are actually built, e.g.:

/src/CMakeLists.txt:
OPTION(BUILD_LIBS "Build libs" ON)
OPTION(BUILD_APPS "Build apps" ON)
IF(BUILD_LIBS)
    ADD_SUBDIRECTORY(libs)
ENDIF()
IF(BUILD_APPS)
    ADD_SUBDIRECTORY(apps)
ENDIF()

So, you can say "cmake /src" to build libraries and applications, or
"cmake -DBUILD_APPS=OFF /src" to build libraries only etc., and in
any case, you may refer safely to ${CMAKE_SOURCE_DIR}/cmake from
each of your projects' CMakeLists.txt.

Regards,

Michael

>>> add_definitions(-FI ${WIN32_SPEC})
>>>
>>>
>>> But when including this central file (find_package) the variable
>> CMAKE_CURRENT_SOURCE_DIR
>>> changes and then the path and filename of the header is wrong.
>>>
>>>
>>>
>>> How to proceed best?
>>> Can I avoid that for those "set" statement the variable is not
>> overwritten by those
>>> files including this central makefile?
>>
>> You may use a CACHED variable
>> set(WIN32_SPEC ${PROJECT_SOURCE_DIR}/libs/global/win32_spec.h CACHE
>> FILEPATH "Central Include")
>>
>> the first calling this will set the value then other set will be
>> ignored.
>> If you want to override a CACHE var value you'll have to use FORCE set
>> option.
>>
>>
>>
>> --
>> Erk
>> Membre de l'April - « promouvoir et défendre le logiciel libre » -
>> http://www.april.org
> 
> Thomas Lehmann
> Scrum Master
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