# CMP0092

MSVC warning flags are not in `CMAKE_<LANG>_FLAGS` by default.

When using MSVC-like compilers in CMake 3.14 and below, warning flags like `/W3` are added to `CMAKE_<LANG>_FLAGS` by default. This is problematic for projects that want to choose a different warning level programmatically. In particular, it requires string editing of the `CMAKE_<LANG>_FLAGS` variables with knowledge of the CMake builtin defaults so they can be replaced.

CMake 3.15 and above prefer to leave out warning flags from the value of `CMAKE_<LANG>_FLAGS` by default.

This policy provides compatibility with projects that have not been updated to expect the lack of warning flags. The policy setting takes effect as of the first `project()` or `enable_language()` command that initializes `CMAKE_<LANG>_FLAGS` for a given lanuage `<LANG>`.

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 MSVC warning flags in the default `CMAKE_<LANG>_FLAGS` cache entries. The `NEW` behavior for this policy is to not place MSVC warning flags in the default cache entries.

This policy was introduced in CMake version 3.15. Use the `cmake_policy()` command to set it to `OLD` or `NEW` explicitly. Unlike many policies, CMake version 3.15.0-rc1 does not warn when this policy is not set and simply uses `OLD` behavior.

Note

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