C ++ 11等效于boost :: date_time :: not_a_date_time是什么？ [英] What is the C++11 equivalent to boost::date_time::not_a_date_time?

问题描述

我正在修改一个旧项目，同时我在更新一些内容以将其升级到C ++ 11。

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

想要用std :: chrono中的新功能替换boost :: date_time的各种用法。但是我不知道boost :: date_time :: not_a_date_time的C ++ 11等价物是什么。

I'd like to replace various uses of boost::date_time with the new functionality in std::chrono. But I cannot figure out what is the C++11 equivalent of boost::date_time::not_a_date_time.

在C ++ 11中没有等价物来指示

Isn't there an equivalent in C++11 to indicate that a time_point variable hasn't yet been assigned, or doesn't contain a valid timestamp?

推荐答案

boost :: date_time 在内部使用整数时间表示，并在 boost / date_time / int_adapter.hpp ：

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;
}

本质上，它保留某些整数值具有特殊含义。

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

但是，正如其他人指出的那样， std :: chrono 不提供这些特殊值（只有 min 和 max 个函数）；和 std :: numeric_limits 也不是专门的（请参见为什么std :: numeric_limits< seconds> :: max（）返回0？）。

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的答案提供了一种可能的解决方法，但请注意，由于 std :: chrono 类不会指定此类语义，将NaN时间戳或持续时间交给您自己未编写的任何函数，很可能会触发未定义的行为。

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.

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