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

If !m.ok(), inserts unsigned(m) followed by " is not a valid month" to os. Otherwise, forms a std::basic_string<CharT> s consisting of the abbreviated month name for the month represented by m, determined using the locale associated with os, and inserts s into os.

Equivalent to.

return os << (m.ok() ?
std::format(os.getloc(), STATICALLY_WIDEN<CharT>("{:L%b}"), m) :
std::format(os.getloc(), STATICALLY_WIDEN<CharT>("{} is not a valid month"), unsigned(m)));

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

Return value



This operator<< is primarily intended for debugging use. For control over formatting, use std::format.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2372R3 C++20 the given locale was used by default L is needed to use the given locale

See also

stores formatted representation of the arguments in a new string
(function template)
specialization of std::formatter that formats a month according to the provided format
(class template specialization)

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