< cpp‎ | chrono‎ | day
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

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.

[edit] Return value


[edit] 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';

Possible output:

42 is not a valid day
00 is not a valid day

[edit] See also

stores formatted representation of the arguments in a new string
(function template) [edit]
formatting support for day
(class template specialization) [edit]