Getting ready

For this example, we will modify the hello-world.cpp example code from Chapter 1, From a Simple Executable to Libraries, Recipe 1, Compiling a single source file into an executable:

#include <cstdlib>
#include <iostream>
#include <string>

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
}

int main() {
  std::cout << say_hello() << std::endl;
  return EXIT_SUCCESS;
}