New in version 3.20.

MSVC RTTI flag /GR is not added to CMAKE_CXX_FLAGS by default.

When using MSVC-like compilers in CMake 3.19 and below, the RTTI flag /GR is added to CMAKE_CXX_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 CMAKE_CXX_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 CMAKE_CXX_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 project() or enable_language() command that initializes CMAKE_CXX_FLAGS.


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 CMAKE_CXX_FLAGS cache entry. The NEW behavior for this policy is to not place the MSVC /GR flag in the default cache entry.

This policy was introduced in CMake version 3.20. It may be set by cmake_policy() or cmake_minimum_required(). If it is not set, CMake does not warn, and uses OLD behavior.


The OLD behavior of a policy is deprecated by definition and may be removed in a future version of CMake.