c++ - 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/标记值。我怎么可能那样做？

Answer 1

您可以使用 boost::optional (或 std::optional，如果您支持 C++17) 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.)