ceph/src/boost/libs/optional/doc/14_io.qbk

   1
   2 [section IO operators]
   3
   4 It is possible to use `optional<T>` with IO streams, provided that `T` can be used with streams. IOStream operators are defined in a separate header.
   5
   6 ``
   7 #include <iostream>
   8 #include <boost/optional/optional_io.hpp>
   9
  10 int main()
  11 {
  12   boost::optional<int> o1 = 1, oN = boost::none;
  13   std::cout << o1;
  14   std::cin >> oN;
  15 }
  16 ``
  17
  18 The current implementation does not guarantee any particular output. What it guarantees is that if streaming out and then back in `T` gives the same value, then streaming out and then back in `optional<T>` will also give back the same result:
  19
  20 ``
  21 #include <cassert>
  22 #include <sstream>
  23 #include <boost/optional/optional_io.hpp>
  24
  25 int main()
  26 {
  27   boost::optional<int> o1 = 1, oN = boost::none;
  28   boost::optional<int> x1, x2;
  29   std::stringstream s;
  30   s << o1 << oN;
  31   s >> x1 >> x2;
  32   assert (o1 == x1);
  33   assert (oN == x2);
  34 }
  35 ``
  36
  37 [endsect]