Size of boost::optional

boost_optional_size.cc

#include <iostream>
#include <memory>
#include <string>
#include "boost/optional.hpp"

int main() {
  std::unique_ptr<std::string> ptr(new std::string("A"));
  boost::optional<std::string> opt_empty;
  boost::optional<std::string> opt_full("A");
  std::cout << "ptr:       " << sizeof(ptr) << '\n';
  std::cout << "*ptr:      " << sizeof(*ptr) << '\n';
  std::cout << "opt_empty: " << sizeof(opt_empty) << '\n';
  std::cout << "opt_full:  " << sizeof(opt_full) << '\n';
  std::cout << "*opt_full: " << sizeof(*opt_full) << '\n';
  return 0;
}

MSVC 2012 x64 Release output:

ptr:       8
*ptr:      32
opt_empty: 40
opt_full:  40
*opt_full: 32

MSVC 2012 x64 Debug output:

ptr:       8
*ptr:      40
opt_empty: 48
opt_full:  48
*opt_full: 40