[CMake] CMake command line arguments

[Gabriel Petrovay]

In order to build the project the users have to land on a doku page or
a README.FIRST anyway. There we can give the command instead of
documenting how this behaves with different generators. So I think
this is a good tradeoff.

On Mon, Mar 7, 2011 at 1:06 PM, Michael Hertling <mhertling at online.de> wrote:
> On 03/07/2011 12:37 PM, Gabriel Petrovay wrote:
>> Thanks for the tips, Michael.
>>
>> We will do so, using project specific BUILD_TYPE and INSTALL_PREFIX.
>
> However, the downside of this approach is that your project's users
> should not refer to the well-known CMake variables CMAKE_BUILD_TYPE
> and CMAKE_INSTALL_PREFIX anymore - possibly an issue to consider.
>
>> On Mon, Mar 7, 2011 at 12:20 PM, Michael Hertling <mhertling at online.de> wrote:
>>> On 03/07/2011 11:33 AM, Michael Hertling wrote:
>>>> On 03/06/2011 12:12 PM, Gabriel Petrovay wrote:
>>>>> Hi,
>>>>>
>>>>> Is there a way to read the arguments that were passed to CMake from
>>>>> inside a CMakeLists.txt file?
>>>>>
>>>>> There is a problem that some generators (like "NMake Makefiles") set a
>>>>> default value for certain variables (like CMAKE_BUILD_TYPE=Debug,
>>>>> CMAKE_INSTALL_PREFIX=C:\Program Files\${CMAKE_PROJECT_NAME})
>>>>>
>>>>> From inside CMake one can not set up a different default value if the
>>>>> user does not specify it with a -D option. This is because
>>>>> IF(CMAKE_BUILD_TYPE) will always be true because of the default set by
>>>>> the generator ("NMake Makefiles").
>>>>>
>>>>> There was this guy having the same problem:
>>>>> http://www.mail-archive.com/cmake@cmake.org/msg09640.html
>>>>>
>>>>> Any solution how one can solve this? Reading the arguments passed to
>>>>> CMake would be one, but I find no documentation/example/google_result
>>>>> for this.
>>>>>
>>>>>
>>>>> Thanks!
>>>>
>>>> Scanning the command line for user-supplied settings wouldn't be
>>>> reliable because your project might also be configured via a GUI.
>>>>
>>>> Furthermore, even an empty CMAKE_BUILD_TYPE variable may denote a
>>>> valid build type, so there's no robust criterion to decide when to
>>>> set a default value by examining this variable alone. Instead, you
>>>> might use another variable, say ${PROJECT_NAME}_BUILD_TYPE, and do:
>>>>
>>>> IF(NOT DEFINED ${PROJECT_NAME}_BUILD_TYPE)
>>>>     SET(${PROJECT_NAME}_BUILD_TYPE "CUSTOM")
>>>> ENDIF()
>>>> SET(CMAKE_BUILD_TYPE "${${PROJECT_NAME}_BUILD_TYPE}")
>>>
>>> Alternatively, you might do:
>>>
>>> SET(${PROJECT_NAME}_BUILD_TYPE "CUSTOM"
>>>    CACHE STRING "${PROJECT_NAME} Build Type")
>>> SET(CMAKE_BUILD_TYPE "${${PROJECT_NAME}_BUILD_TYPE}")
>>>
>>> So, you'll have at least your project's own build type in the cache -
>>> and, thus, in the GUIs - along with the documenting comment while the
>>> cached value of CMAKE_BUILD_TYPE is still not the one that's actually
>>> used.
>
> If you say
>
> SET(CMAKE_BUILD_TYPE "${${PROJECT_NAME}_BUILD_TYPE}"
>    CACHE STRING "CMake Build Type" FORCE)
>
> here, the cached value of CMAKE_BUILD_TYPE will equal the value in the
> current scope again. Obviously, I'm quite unconcentrated today... ;-)
>
>>>> In this way, an undefined ${PROJECT_NAME}_BUILD_TYPE results in a
>>>> default CMAKE_BUILD_TYPE on behalf of the CMakeLists.txt file. Of
>>>> course, you should document that variable and urge your project's
>>>> users to not directly use CMAKE_BUILD_TYPE anymore; perhaps, you
>>>> should even hide the latter in a GUI by marking it as advanced.
>>>>
>>>> With regard to CMAKE_INSTALL_PREFIX, you could do the same - or use
>>>> CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT, as a robust criterion,
>>>> to see whether the user has supplied a value explicitly. Note that
>>>> there're additional aspects to consider if the CMakeLists.txt file
>>>> is to write that variable's value to the cache, cf. [1] et seq.
>>>>
>>>> Regards,
>>>>
>>>> Michael
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-- 
MSc Gabriel Petrovay
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