The code for this recipe is available at https://github.com/dev-cafe/cmake-cookbook/tree/v1.0/chapter-02/recipe-01. The recipe is valid with CMake version 3.5 (and higher) and has been tested on GNU/Linux, macOS, and Windows.
CMake is a set of cross-platform tools. Nevertheless, it can be very useful to know on which operating system (OS) the configuration or build step is executed. Such OS discovery can be used either to tweak CMake code for a particular OS, to enable conditional compilation depending on the OS, or to use compiler-specific extensions if available or necessary. In this recipe, we will demonstrate how to use CMake to detect the OS with an example that does not require compilation of any source code. For simplicity, we will only consider the configuration step.
