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        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.
      
#include <iostream> #include <boost/optional/optional_io.hpp> int main() { boost::optional<int> o1 = 1, oN = boost::none; std::cout << o1; std::cin >> oN; }
        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:
      
#include <cassert> #include <sstream> #include <boost/optional/optional_io.hpp> int main() { boost::optional<int> o1 = 1, oN = boost::none; boost::optional<int> x1, x2; std::stringstream s; s << o1 << oN; s >> x1 >> x2; assert (o1 == x1); assert (oN == x2); }