std::chrono::operator<<(std::chrono::day) - cppreference.com (original) (raw)
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
os
[edit] Example
#include #include 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