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 ...
