[CMake] Changing /W3 to /W4 does not update CMakeCache.txt

[Craig Scott]

See the first item on the following article for guidance on how to combine
cache and non-cache values for CMAKE_CXX_FLAGS:

http://voices.canonical.com/jussi.pakkanen/2013/03/26/a-list-of-common-cmake-antipatterns/


On Fri, Feb 3, 2017 at 12:19 PM, Andrew Maclean <andrew.amaclean at gmail.com>
wrote:

> Craig,
>    Thanks for this, I had forgotten the distinction between non-cached
> variables and cached variables
>
> I guess the issue is that whilst it is possible to modify the cached
> entry, it will never be used since the non-cached variable will always
> override it whenever cmake is invoked.
>
> Andrew
>
> On Fri, Feb 3, 2017 at 10:26 AM, Craig Scott <craig.scott at crascit.com>
> wrote:
>
>> Your CMakeLists.txt file is modifying the *non-cache* variable
>> CMAKE_CXX_FLAGS. During CMake processing, a non-cache variable will
>> override a cache variable of the same name, but modifying a non-cache
>> variable won't update the cache. CMake is working as designed with regard
>> to the handling of CMAKE_CXX_FLAGS here, your expectation of the cache
>> being updated to reflect your changes to the non-cache variable is the
>> source of the confusion. Please review the following link which describes
>> this in more detail:
>>
>> https://cmake.org/cmake/help/latest/manual/cmake-language.7.
>> html#variables
>>
>>
>> On Fri, Feb 3, 2017 at 10:01 AM, Andrew Maclean <
>> andrew.amaclean at gmail.com> wrote:
>>
>>> Consider the attached CMakeLists.txt script.
>>>
>>> When run, CMAKE_CXX_FLAGS is updated correctly, however the line:
>>> CMAKE_CXX_FLAGS:STRING=/DWIN32 /D_WINDOWS /W3 /GR /EHsc
>>> in CMakeCache.txt is never updated.
>>>
>>> However the build instructions e.g build.ninja reflect the correct
>>> command:
>>>  FLAGS = /DWIN32 /D_WINDOWS /W4 /GR /EHsc /D_DEBUG /MDd /Zi /Ob0 /Od
>>> /RTC1
>>> Similarly for the Visual Studio Build.
>>>
>>> I see this behaviour in my own code and also in VTK.
>>>
>>> Is there a reason why CMakeCache.txt does not get the update?
>>>
>>> Andrew
>>>
>>>
>>> --
>>> ___________________________________________
>>> Andrew J. P. Maclean
>>>
>>> ___________________________________________
>>>
>>> --
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>>
>>
>>
>> --
>> Craig Scott
>> Melbourne, Australia
>> https://crascit.com
>>
>
>
>
> --
> ___________________________________________
> Andrew J. P. Maclean
>
> ___________________________________________
>



-- 
Craig Scott
Melbourne, Australia
https://crascit.com
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