[CMake] Appending to CMAKE_CXX_FLAGS

[Michael Jackson]

Just to be clear I _only_ need it when the generator is Visual Studio so I did the following:

 

if(MSVC_IDE)

  add_compile_options(/MP)

endif()

 

>From a clean build directory that did not add it to the CMAKE_CXX_FLAGS when viewed in CMake-Gui.

 

--

Mike Jackson 

 

From: Marc CHEVRIER <marc.chevrier at gmail.com>
Date: Tuesday, September 11, 2018 at 1:28 PM
To: Michael Jackson <mike.jackson at bluequartz.net>
Cc: CMake <cmake at cmake.org>
Subject: Re: [CMake] Appending to CMAKE_CXX_FLAGS

 

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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