# cmake_minimum_required

Require a minimum version of cmake.

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

New in version 3.12: The optional `<policy_max>` version.

Sets the minimum required version of cmake for a project. Also updates the policy settings as explained below.

`<min>` and the optional `<policy_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 `<policy_max>` version, if specified, must be at least the `<min>` version and affects policy settings as described in Policy Settings. 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>`.

This command will set the value of the `CMAKE_MINIMUM_REQUIRED_VERSION` variable to `<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. For example, the `CMAKE_MINIMUM_REQUIRED_VERSION` variable won't be set in the calling scope. Functions do not introduce their own policy scope though, so policy settings of the caller will be affected (see below). Due to this mix of things that do and do not affect the calling scope, calling `cmake_minimum_required()` inside a function is generally discouraged.

## 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.