[CMake] Appending to CMAKE_CXX_FLAGS

[Marc CHEVRIER]

If you set directory property at the top level CMakeList.txt, before any
target definition, all targets will inherit this value.

And, because property 'COMPILE_OPTIONS' supports generator expressions (see
https://cmake.org/cmake/help/v3.12/manual/cmake-generator-expressions.7.html),
you can specify:

add_compile_options("$<$<CXX_COMPILER_ID:MSVC>:/MP>")


Le mar. 11 sept. 2018 à 19:19, Michael Jackson <mike.jackson at bluequartz.net>
a écrit :

> Hmm. The idea for the “/MP” flags for those that don’t use Visual Studio
> is that it will inform the compiler to use all the cores on the system to
> compile. Much like Ninja does automatically and “make -jN” does for
> makefiles.
>
> Essentially I want to automatically add the “/MP” flag anytime that I
> configure using Visual Studio (2015/2017) as the generator. I guess I could
> put the append string fairly high up in the CMake hierarchy. I am not
> seeing a property (from the first link you sent) that would allow me to do
> that.
>
>
>
> --
>
> Michael Jackson | Owner, President
>
>       BlueQuartz Software
>
> [e] mike.jackson at bluequartz.net
>
> [w] www.bluequartz.net
>
>
>
> *From: *Marc CHEVRIER <marc.chevrier at gmail.com>
> *Date: *Tuesday, September 11, 2018 at 1:04 PM
> *To: *Michael Jackson <mike.jackson at bluequartz.net>
> *Cc: *CMake <cmake at cmake.org>
> *Subject: *Re: [CMake] Appending to CMAKE_CXX_FLAGS
>
>
>
> The best approach is to use properties (see
> https://cmake.org/cmake/help/git-master/manual/cmake-properties.7.html).
>
>
>
> At directory level and target level you can use property
> 'COMPILE_OPTIONS'.  These properties can be updated using, respectively
> 'add_compile_options' and 'target_compile_options'.
>
>
>
> Be aware that variable 'CMAKE_CXX_FLAGS' is a string so to extend it you
> have to use:
>
> string(APPEND CMAKE_CXX_FLAGS "flag1 flag2")
>
>
>
>
>
> Le mar. 11 sept. 2018 à 17:58, Michael Jackson <
> mike.jackson at bluequartz.net> a écrit :
>
> What is the “modern” way to append to CMAKE_CXX_FLAGS? This is the logic
> that I would like:
>
>
>
> If (MSVC)
>
>                 Set(CMAKE_CXX_FLAGS ${ CMAKE_CXX_FLAGS} “/MP”)
>
> Endif()
>
>
>
> I have always heard that appending to the compile flags in this way is
> “bad”. What is the best practice for doing this?
>
>
>
> Thanks
>
> --
>
> Michael Jackson | Owner, President
>
>       BlueQuartz Software
>
> [e] mike.jackson at bluequartz.net
>
> [w] www.bluequartz.net
>
> --
>
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