[CMake] CMake command line arguments

[Michael Hertling]

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.

> 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