[CMake] Understanding default Visual Studio compiler flags

[Neal Kruis]

Hi all,

I'm hoping someone can clarify some confusion I have regarding the flags
used in Visual Studio Cmake builds.

For example, in a release build, there are the defaults:

CMAKE_CXX_FLAGS:STRING=/DWIN32 /D_WINDOWS /W3 /GR /EHsc
CMAKE_CXX_FLAGS_RELEASE:STRING=/MD /O2 /Ob2 /DNDEBUG

We can obviously append to or modify these within our CMakeLists.txt files.
However, my actual build flags look like this:

/nologo /W3 /WX- /O2 /Ob2 /Oy- /D WIN32 /D _WINDOWS /D NDEBUG /D
"CMAKE_INTDIR=\"Release\"" /D _MBCS /Gm- /EHsc /MT /GS /fp:precise
/Zc:wchar_t /Zc:forScope /Zc:inline /GR /Fo"PROJECT.DIR\RELEASE\\"
/Fd"PROJECT.DIR\RELEASE\VC140.PDB" /Gd /TP /analyze-

Where are all these other flags coming from? Some of these I appreciate are
necessary for the CMake mechanics to work, but what if (for whatever
reason) I wanted to remove one of the other flags that isn't defined by
CMAKE_CXX_FLAGS or CMAKE_CXX_FLAGS_RELEASE (e.g., /Zc:wchar_t)?

Can Cmake users override the values from the default flag table
<https://gitlab.kitware.com/cmake/cmake/blob/master/Source/cmVS141CLFlagTable.h>
?

Regards,

Neal Kruis
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