27 Time library [time]

27.8 The civil calendar [time.cal]

27.8.3 Class day [time.cal.day]

27.8.3.3 Non-member functions [time.cal.day.nonmembers]

constexpr bool operator==(const day& x, const day& y) noexcept;
Returns: unsigned{x} == unsigned{y}.
constexpr strong_ordering operator<=>(const day& x, const day& y) noexcept;
Returns: unsigned{x} <=> unsigned{y}.
constexpr day operator+(const day& x, const days& y) noexcept;
Returns: day(unsigned{x} + y.count()).
constexpr day operator+(const days& x, const day& y) noexcept;
Returns: y + x.
constexpr day operator-(const day& x, const days& y) noexcept;
Returns: x + -y.
constexpr days operator-(const day& x, const day& y) noexcept;
Returns: days{int(unsigned{x}) - int(unsigned{y}).
template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const day& d);
Effects: Equivalent to:
return os << (d.ok() ?
  format(STATICALLY-WIDEN<charT>("{:%d}"), d) :
  format(STATICALLY-WIDEN<charT>("{:%d} is not a valid day"), d));
template<class charT, class traits, class Alloc = allocator<charT>> basic_istream<charT, traits>& from_stream(basic_istream<charT, traits>& is, const charT* fmt, day& d, basic_string<charT, traits, Alloc>* abbrev = nullptr, minutes* offset = nullptr);
Effects: Attempts to parse the input stream is into the day d using the format flags given in the NTCTS fmt as specified in [time.parse].
If the parse fails to decode a valid day, is.setstate(ios_­base​::​failbit) shall be called and d shall not be modified.
If %Z is used and successfully parsed, that value will be assigned to *abbrev if abbrev is non-null.
If %z (or a modified variant) is used and successfully parsed, that value will be assigned to *offset if offset is non-null.
Returns: is.
constexpr day operator""d(unsigned long long d) noexcept;
Returns: day{static_­cast<unsigned>(d)}.