# cmake_minimum_required

Set the minimum required version of cmake for a project and update Policy Settings to match the version given:

    cmake_minimum_required(VERSION <min>[...<max>] [FATAL_ERROR])

`<min>` and the optional `<max>` are each CMake versions of the form `major.minor[.patch[.tweak]]`, and the `...` is literal.

If the running version of CMake is lower than the `<min>` required version it will stop processing the project and report an error. The optional `<max>` version, if specified, must be at least the `<min>` version and affects policy settings as described below. If the running version of CMake is older than 3.12, the extra `...` dots will be seen as version component separators, resulting in the `...<max>` part being ignored and preserving the pre-3.12 behavior of basing policies on `<min>`.

The `FATAL_ERROR` option is accepted but ignored by CMake 2.6 and higher. It should be specified so CMake versions 2.4 and lower fail with an error instead of just a warning.

Note

Call the `cmake_minimum_required()` command at the beginning of the top-level `CMakeLists.txt` file even before calling the `project()` command. It is important to establish version and policy settings before invoking other commands whose behavior they may affect. See also policy `CMP0000`.

Calling `cmake_minimum_required()` inside a `function()` limits some effects to the function scope when invoked. Such calls should not be made with the intention of having global effects.

## Policy Settings

The `cmake_minimum_required(VERSION)` command implicitly invokes the `cmake_policy(VERSION)` command to specify that the current project code is written for the given range of CMake versions. All policies known to the running version of CMake and introduced in the `<min>` (or `<max>`, if specified) version or earlier will be set to use `NEW` behavior. All policies introduced in later versions will be unset. This effectively requests behavior preferred as of a given CMake version and tells newer CMake versions to warn about their new policies.

When a `<min>` version higher than 2.4 is specified the command implicitly invokes:

    cmake_policy(VERSION <min>[...<max>])

which sets CMake policies based on the range of versions specified. When a `<min>` version 2.4 or lower is given the command implicitly invokes:

    cmake_policy(VERSION 2.4[...<max>])

which enables compatibility features for CMake 2.4 and lower.