CMake Cookbook

How it works

The interesting part in the hello-world.cpp example is the conditional compilation based on the preprocessor definitions IS_WINDOWS, IS_LINUX, or IS_MACOS:

std::string say_hello() {#ifdef IS_WINDOWS  return std::string("Hello from Windows!");#elif IS_LINUX  return std::string("Hello from Linux!");#elif IS_MACOS

  return std::string("Hello from macOS!");#else  return std::string("Hello from an unknown system!");#endif}

These definitions are defined at configure time by CMake in CMakeLists.txt by using target_compile_definitions before being passed on to the preprocessor. We could have achieved a more compact expression without repeating if-endif statements and we will demonstrate this refactoring in the next recipe. We could also ...