What is the C++11 equivalent to boost::date_time::not_a_date_time?

前端 未结 2 1256
独厮守ぢ
独厮守ぢ 2021-01-06 18:03

I\'m modifying an old project, and at the same time I\'m updating several things to bring it up to C++11.

I\'d like to replace various uses of boost::date_time with

相关标签:
2条回答
  • 2021-01-06 18:14

    Given the fact that it exists as part of a group

    bool is_infinity() const
    bool is_neg_infinity() const
    bool is_pos_infinity() const
    bool is_not_a_date_time() const
    

    it is pretty clear that this is done by using a floating-point type for the internal representation and setting the value to a NaN (not-a-number).

    In std::chrono, the representation type is required to be an arithmetic type. Floating-point types therefore qualify, and you can use the same trick.

    Given a std::duration, you could then test it using

    std::isnan(dur.count())
    

    (Naturally, you should use a quiet NaN value, not a signalling NaN, so you don't trigger floating-point traps)

    0 讨论(0)
  • 2021-01-06 18:17

    boost::date_time uses integer time representations internally, and defines the special values inside boost/date_time/int_adapter.hpp:

    static const int_adapter  pos_infinity()
    {
      return (::std::numeric_limits<int_type>::max)();
    }
    static const int_adapter  neg_infinity()
    {
      return (::std::numeric_limits<int_type>::min)();
    }
    static const int_adapter  not_a_number()
    {
      return (::std::numeric_limits<int_type>::max)()-1;
    }
    static  int_adapter max BOOST_PREVENT_MACRO_SUBSTITUTION ()
    {
      return (::std::numeric_limits<int_type>::max)()-2;
    }
    static  int_adapter min BOOST_PREVENT_MACRO_SUBSTITUTION ()
    {
      return (::std::numeric_limits<int_type>::min)()+1;
    }
    

    Essentially, it reserves certain integer values to have special meanings.

    However, as others have pointed out, std::chrono does not offer these special values (there are only min and max functions); and std::numeric_limits is also not specialized (see Why does std::numeric_limits<seconds>::max() return 0?).

    Ben Voigt's answer presents a possible workaround, but be aware that since the std::chrono classes do not specify such semantics, handing a NaN timestamp or duration to any function you did not write yourself is likely going to trigger undefined behaviour.

    0 讨论(0)
提交回复
热议问题