Set the minimum required version of cmake for a project.

cmake_minimum_required(VERSION major[.minor[.patch[.tweak]]]

If the current version of CMake is lower than that required it will stop processing the project and report an error. When a version higher than 2.4 is specified the command implicitly invokes

cmake_policy(VERSION major[.minor[.patch[.tweak]]])

which sets the cmake policy version level to the version specified. When version 2.4 or lower is given the command implicitly invokes

cmake_policy(VERSION 2.4)

which enables compatibility features for CMake 2.4 and lower.

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.