std::chrono::year_month_day_last:: ok

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C-style date and time
std::chrono::year_month_day_last
constexpr bool ok ( ) const noexcept ;
(since C++20)

Checks if * this represents a valid date. Because a year_month_day_last represents the last day of a particular month, it represents a valid date as long as the year and month are valid.

Return value

year ( ) . ok ( ) && month ( ) . ok ( )

Example

Run this code 
#include <cassert>
#include <chrono>
 
int main()
{
    auto ymdl{std::chrono::last/11/2020};
    assert(ymdl.ok());
    ymdl = std::chrono::year(2020)/std::chrono::month(13)/std::chrono::last;
    assert(not ymdl.ok());
}
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