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89 lines
2.9 KiB
C++
89 lines
2.9 KiB
C++
/** Support for date/time values.
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*
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* At the moment this supports dates, but not times.
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*/
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#ifndef PQXX_H_TIME
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#define PQXX_H_TIME
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#if !defined(PQXX_HEADER_PRE)
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# error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
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#endif
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#include <chrono>
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#include <cstdlib>
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#include "pqxx/internal/concat.hxx"
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#include "pqxx/strconv.hxx"
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#if defined(PQXX_HAVE_YEAR_MONTH_DAY)
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namespace pqxx
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{
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using namespace std::literals;
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template<>
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struct nullness<std::chrono::year_month_day>
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: no_null<std::chrono::year_month_day>
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{};
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/// String representation for a Gregorian date in ISO-8601 format.
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/** @warning Experimental. There may still be design problems, particularly
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* when it comes to BC years.
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*
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* PostgreSQL supports a choice of date formats, but libpqxx does not. The
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* other formats in turn support a choice of "month before day" versus "day
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* before month," meaning that it's not necessarily known which format a given
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* date is supposed to be. So I repeat: ISO-8601-style format only!
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*
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* Invalid dates will not convert. This includes February 29 on non-leap
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* years, which is why it matters that `year_month_day` represents a
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* _Gregorian_ date.
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*
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* The range of years is limited. At the time of writing, PostgreSQL 14
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* supports years from 4713 BC to 294276 AD inclusive, and C++20 supports
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* a range of 32767 BC to 32767 AD inclusive. So in practice, years must fall
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* between 4713 BC and 32767 AD, inclusive.
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*
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* @warning Support for BC (or BCE) years is still experimental. I still need
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* confirmation on this issue: it looks as if C++ years are astronomical years,
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* which means they have a Year Zero. Regular BC/AD years do not have a year
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* zero, so the year 1 AD follows directly after 1 BC.
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*
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* So, what to our calendars (and to PostgreSQL) is the year "0001 BC" seems to
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* count as year "0" in a `std::chrono::year_month_day`. The year 0001 AD is
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* still equal to 1 as you'd expect, and all AD years work normally, but all
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* years before then are shifted by one. For instance, the year 543 BC would
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* be -542 in C++.
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*/
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template<> struct PQXX_LIBEXPORT string_traits<std::chrono::year_month_day>
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{
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[[nodiscard]] static zview
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to_buf(char *begin, char *end, std::chrono::year_month_day const &value)
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{
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return generic_to_buf(begin, end, value);
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}
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static char *
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into_buf(char *begin, char *end, std::chrono::year_month_day const &value);
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[[nodiscard]] static std::chrono::year_month_day
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from_string(std::string_view text);
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[[nodiscard]] static std::size_t
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size_buffer(std::chrono::year_month_day const &) noexcept
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{
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static_assert(int{(std::chrono::year::min)()} >= -99999);
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static_assert(int{(std::chrono::year::max)()} <= 99999);
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return 5 + 1 + 2 + 1 + 2 + std::size(s_bc) + 1;
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}
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private:
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/// The "BC" suffix for years before 1 AD.
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static constexpr std::string_view s_bc{" BC"sv};
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};
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} // namespace pqxx
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#endif // PQXX_HAVE_YEAR_MONTH_DAY
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#endif
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