[CMake] Set CMAKE_<LANG>_FLAGS_* and overriding

[Williams, Norman K]

It occurs to me that if your project requires C++11, you need something
more flexible and intelligent. I don't remember what mailing list I saw it
on (ITK?) but there is some discussion about detecting C++-11 and what the
most portable way to do that is.

You can check for specific compilers and set appropriate flags, and run
test-compile probes to determine if they're accepted.
A good exemplar to look at is in ITK:

http://bit.ly/1a0veeb ITKSetStandardCompilerFlags.cmake
http://bit.ly/16B6p8C ITK_CheckCCompilerFlag.cmake


http://bit.ly/16B6vgu ITK_CheckCCompilerFlag.cmake

Since ITK is an open source project, you can just copy and use these;
there are macros in there you can call to check if particular compiler
flags to use.

--
Kent Williams norman-k-williams at uiowa.edu






On 9/17/13 4:59 AM, "Cristian Bidea" <cristi at king.com> wrote:

>Hi David
>
>You have a number of options here:
>
>1. You can pass the additional compile flag trough another variable
>instead of trying to override CMAKE_CXX_FLAGS.
>
>cmake .. -DFREEBSD_FLAG="-stdlib=libc++"
>
>... then in CMakeLists.txt you can set the compile flags as follows:
>
>set (CMAKE_CXX_FLAGS "-std=c++11 ${FREEBSD}")
>
>When the FREBSD option isn't set, then the string would contain just
>"-std=c++11 ".
>
>2. Another way would be to set compile flags depending on the platform
>you're compiling on (that works if you don't do cross compiling):
>
>if ("${CMAKE_SYSTEM_NAME}" STREQUAL "FreeBSD")
>    set (CMAKE_CXX_FLAGS "-std=c++11 -stdlib=libc++")
>else ()
>    set (CMAKE_CXX_FLAGS "-std=c++11")
>endif ()
>
>3. And the third option would be to also preserve the previous value of
>CMAKE_CXX_FLAGS
>
>set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
>
>... so now it doesn't get overriden!
>
>Hope this helps!
>
>-Cristi
>
>On Tue Sep 17 12:40:31 2013, David Demelier wrote:
>> Hello,
>>
>> I'm writing a C++11 project. To enable C++11 it requires some switches,
>> such as -std=c++11.
>>
>> So for the moment, I have in my CMakeLists.txt:
>>
>> set(CMAKE_CXX_FLAGS "-std=c++11")
>>
>> So with that, I'm sure that any build configuration will add this.
>> However, with clang++, you need to pass an additional flag (for FreeBSD
>> especially): -stdlib=libc++.
>>
>> So I would like to be able to do at command line:
>>
>> cmake .. -DCMAKE_CXX_FLAGS="-std=c++11 -stdlib=libc++"
>>
>> But with that, it just ignore my setting and take the one from the
>> CMakeLists.txt
>>
>> What is the correct way to:
>>
>> * Set CXX flags globally, for any type of configuration
>> * Let them be overriden?
>>
>> Regards,
>>
>> David.
>> --
>>
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>
>Powered by www.kitware.com
>
>Please keep messages on-topic and check the CMake FAQ at:
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>
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