std::chrono::time_point 无效值

Question

boost/std :: chrono::time_point my_time_point( /* invalid value */ );

我需要存储一个无效/无意义/哨兵值。我怎么可能这样做？

Answer 1

你可以使用boost::optional（或者std::optional如果你支持C++17）来表示chrono::time_point的无效状态：

#include <chrono>
#include <boost/optional.hpp>

int main()
{
    using my_clock = std::chrono::system_clock;
    using my_time_point = std::chrono::time_point<my_clock>;

    boost::optional<my_time_point> maybe_time_point;

    // Set to invalid value:
    maybe_time_point = boost::none;

    // If 'maybe_time_point' is valid...
    if(maybe_time_point) 
    { 
        auto inner_value = *maybe_time_point;
        /* ... */
    }
    else { /* ... */ }
}

(You can run it on wandbox.)

Answer 2

我有同样的要求，结果发现有一个优雅的解决方案。如果您可以将 TimePoint 设置为未来 {Fri Apr 11 23:47:16 2262} 的不合理的大值，那么这样做应该很简单。

using Clock = std::chrono::high_resolution_clock;
using TimePoint = std::chrono::time_point<Clock>;
constexpr TimePoint invalidTime_k = TimePoint::max();

TimePoint my_time_point = invalidTime_k;

警告：此帖子将导致 Y2262 问题。但到那时，我们应该在标准中有更好的类型。