CMake/Help/policy/CMP0117.rst

CMP0117
-------

.. versionadded:: 3.20

MSVC RTTI flag ``/GR`` is not added to
:variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` by default.

When using MSVC-like compilers in CMake 3.19 and below, the RTTI flag
``/GR`` is added to :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` by
default.  This behavior is left from support for MSVC versions from Visual
Studio 2003 and below that did not enable RTTI by default.  It is no longer
necessary.  Furthermore, it is problematic for projects that want to change
to ``/GR-`` programmatically.  In particular, it requires string editing of
the :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` variable with knowledge
of the CMake builtin default so it can be replaced.

CMake 3.20 and above prefer to leave out ``/GR`` from the value of
:variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` by default.

This policy provides compatibility with projects that have not been updated
to expect the lack of the ``/GR`` flag.  The policy setting takes effect as
of the first :command:`project` or :command:`enable_language` command that
initializes :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>`.

.. note::

  Once the policy has taken effect at the top of a project for a given
  language, that choice must be used throughout the tree for that language.
  In projects that have nested projects in subdirectories, be sure to
  convert everything together.

The ``OLD`` behavior for this policy is to place the MSVC ``/GR`` flag in the
default :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` cache entry.  The
``NEW`` behavior for this policy is to *not* place the MSVC ``/GR`` flag in
the default cache entry.

.. |INTRODUCED_IN_CMAKE_VERSION| replace:: 3.20
.. |WARNS_OR_DOES_NOT_WARN| replace:: does *not* warn
.. include:: include/STANDARD_ADVICE.rst

.. include:: include/DEPRECATED.rst