std::chrono::year_month_day::ok

 

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std::chrono::year_month_day

成员函数

year_month_day::year_month_day

year_month_day::operator+=year_month_day::operator-=

year_month_day::yearyear_month_day::monthyear_month_day::day

year_month_day::operator sys_daysyear_month_day::operator local_days

year_month_day::ok

非成员函数

operator==operator<=>

operator+operator-

operator<<

from_stream

辅助类

formatter<std::chrono::year_month_day>

hash<std::chrono::year_month_day> (C++26)

 

constexpr bool ok() const noexcept;		(自 C++20 起)

检查此 year_month_day 对象是否表示有效的日历日期。

返回值

true 如果此 year_month_day 对象表示有效的日历日期，即存储的年、月和日值均有效，并且存储的日值在给定年和月的日数范围内。否则 false.

可能的实现

constexpr bool std::chrono::year_month_day::ok() const noexcept { return year().ok() && month().ok() && day().ok() && day() <= (year()/month()/std::chrono::last).day(); }

示例

运行此代码

#include <chrono>
 
int main()
{
    constexpr auto ymd1 {std::chrono::day(1)/std::chrono::July/2020};
    static_assert(ymd1.ok());
 
    constexpr auto ymd2 {std::chrono::year(2020)/7/42};
    static_assert(not ymd2.ok());
 
    constexpr auto ymd3 {std::chrono::February/29/2020}; // ok, leap year
    static_assert(ymd3.ok());
 
    constexpr auto ymd4 = ymd3 + std::chrono::years{1}; // bad, not a leap year
    static_assert(ymd4 == std::chrono::February/29/2021 and not ymd4.ok());
 
    // to fix the bad date we may want to snap to the last day of the month:
    if constexpr (!ymd4.ok())
    {
        constexpr auto ymd = ymd4.year()/ymd4.month()/std::chrono::last;
        static_assert(ymd == std::chrono::February/28/2021 and ymd.ok());
    }
 
    // or we may want to overflow to the next month:
    if constexpr (!ymd4.ok())
    {
        constexpr auto st = std::chrono::sys_time<std::chrono::days>{ymd4};
        constexpr auto ymd = std::chrono::year_month_day{st};
        static_assert(ymd == std::chrono::March/1/2021 and ymd.ok());
    }
}