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

 

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chrono I/O
parse (C++20)
C-style date and time

 

std::chrono::day

Member functions

day::day

day::operator++day::operator--

day::operator+=day::operator-=

day::operator unsigned

day::ok

Nonmember functions

operator==operator<=>

operator+operator-

operator<<

from_stream

operator""d

Helper classes

formatter<std::chrono::day>

 

Defined in header <chrono>
template< class CharT, class Traits > std::basic_ostream<CharT, Traits>& operator<<( std::basic_ostream<CharT, Traits>& os, const std::chrono::day& d );		(since C++20)

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

Run this code

#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';
}

Possible output:

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

See also

format (C++20)	stores formatted representation of the arguments in a new string (function template)
std::formatter<std::chrono::day> (C++20)	formatting support for day (class template specialization)