std::chrono::weekday_indexed:: ok

From cppreference.com
C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
Date and time utilities
Time point
(C++11)
(C++20)
Duration
(C++11)
Clocks
(C++20)
(C++20)
(C++20)
Time of day
(C++20) (C++20)
(C++20) (C++20)
(C++20)

Calendar
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
Time zone
(C++20)
(C++20)
(C++20) (C++20) (C++20) (C++20)
(C++20)
chrono I/O
(C++20)
C-style date and time
std::chrono::weekday_indexed
constexpr bool ok ( ) const noexcept ;
(since C++20)

Checks if the weekday object and the index stored in * this are both valid.

Return value

true if weekday ( ) . ok ( ) == true and index() is in the range [ 1 , 5 ] . Otherwise false .

Example

Run this code 
#include <chrono>
#include <iostream>
 
int main()
{
    std::cout << std::boolalpha;
 
    std::chrono::weekday_indexed wdi{std::chrono::Tuesday[2]};
    std::cout << (wdi.ok()) << ' ';
    wdi = {std::chrono::weekday(42)[2]}; 
    std::cout << (wdi.ok()) << ' ';
    wdi = {std::chrono::Tuesday[-4]}; 
    std::cout << (wdi.ok()) << '\n';
}

Output: 

true false false
Retrieved from " https://en.cppreference.com/mwiki/index.php?title=cpp/chrono/weekday_indexed/ok&oldid=157211 "