std :: chrono :: time_point無效值

Question

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

我需要存儲無效/不符合/標記值。我怎麼可能做到這一點？

Answer 1

您可以使用boost::optional（或std::optional，如果你有C++ 17的支持）代表的chrono::time_point無效狀態：

#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.)