std::chrono:: operator<< (std::chrono::day)

Forms a std:: basic_string < CharT > s consisting of the day value stored in d formatted as a decimal number, with a leading zero if the result would otherwise be a single decimal digit. Then, if ! d. ok ( ) , append " is not a valid day" to the formatted string. Inserts that string into os .

Equivalent to

return os << ( d. ok ( ) ?
std:: format ( STATICALLY_WIDEN < CharT > ( "{:%d}" ) , d ) :
std:: format ( STATICALLY_WIDEN < CharT > ( "{:%d} is not a valid day" ) , d ) ) ;

where STATICALLY_WIDEN < CharT > ( "..." ) is "..." if CharT is char , and L "..." if CharT is wchar_t .

Return value

os

Example

#include <chrono>
#include <iostream>
 
int main()
{
    constexpr std::chrono::day d1{31}, d2{7}, d3{42}, d4{};
    std::cout << d1 << '\n'
              << d2 << '\n'
              << d3 << '\n'
              << d4 << '\n';
}

31
07
42 is not a valid day
00 is not a valid day

See also