[CMake] Using two sets of compiler flags in same build

[Petr Kmoch]

Hi Andre,

I can think of two ways. One is using target properties COMPILE_FLAGS
and COMPILE_DEFINITIONS to setup flags on a per-target basis.
Unfortunately, there's no per-config version of those :-(

Another is to separate your targets into directories added by
add_subdirectory(). I believe you can then override variables in the
subdirectory without affecting the parent directory. Note that these
are parent/subdirectory in CMake sense, they can actually be siblings
or unrelated on disk.

Petr

On Tue, Apr 17, 2012 at 10:01 PM, André Caron <andre.l.caron at gmail.com> wrote:
> Hi all,
>
> I've posted this issue on StackOverflow[1] and have not yet received a
> suitable response, so I thought I'd ask here instead.
>
> Basically, I need to have a single build that uses two sets of
> compiler flags.  One set is used to build native windows applications,
> and the other to build a managed (C++.net) application.  It is my
> understanding that CMake kind of goes out of its way so that compiler
> flags are uniform throughout the project because this is usually the
> Right Thing(TM) -- actually, this is one of the reasons I like CMake.
>
> How can I create a CMake build script so that I have a subset of
> targets that build using a specific set of compiler flags, and another
> subset of targets that build with another set of compiler flags?
> Please keep in mind that I can't "switch" between either set of flags
> like I would for debug and release modes because I'm always building
> all the targets.
>
> I currently have this little helper macro (I understand why this is
> wrong, see below):
>
> # Compile managed (.NET) program.
> macro(add_managed_executable target)
>   # Enable managed C++ extensions.
>   if(NOT ${CMAKE_CXX_FLAGS} MATCHES "/clr")
>     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /clr")
>   endif()
>   # Remove incompatible settings.
>   if(${CMAKE_CXX_FLAGS_DEBUG} MATCHES "/RTC")
>     string(REGEX REPLACE
>       "/RTC(.+)" "" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}"
>     )
>   endif()
>   if(${CMAKE_CXX_FLAGS_DEBUG} MATCHES "/MT")
>     string(REGEX REPLACE
>       "/MT(.+)" "" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}"
>     )
>   endif()
>   if(${CMAKE_CXX_FLAGS_DEBUG} MATCHES "/MD")
>     string(REGEX REPLACE
>       "/MD(.+)" "" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}"
>     )
>   endif()
>   # Add target.
>   add_executable(${target} WIN32 ${ARGN})
> endmacro()
>
> However, as expected, this completely screws up my build because
> changing CMAKE_CXX_FLAGS* affects the other targets, not only the one
> specified in the add_executable() call inside the macro.
>
> Thanks,
> André
>
> [1]: http://stackoverflow.com/q/10167175/313063
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