Copying `std::exception` with an error message

std_exception.cc

#include <iostream>

int main() {
  auto err = std::logic_error("some error");
  std::cout << err.what() << std::endl;

  // using the derived copy constructor
  std::logic_error err2 = err;
  std::cout << err2.what() << std::endl;

  // what() is virtual
  std::exception &err3 = err;
  std::cout << err3.what() << std::endl;

  // This slices the object
  std::exception err4 = err;
  std::cout << err4.what() << std::endl;
}