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Formatting of system clocks ought to be to UTC, not to local time.

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This improves standards conformance of fmt.
This commit is contained in:
Niall Douglas (s [underscore] sourceforge {at} nedprod [dot] com)
2022-12-21 14:23:02 -08:00
committed by Victor Zverovich
parent b90895412f
commit 115001a3b1
3 changed files with 133 additions and 17 deletions
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include/fmt/chrono.h
+46 -2
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@@ -22,6 +22,15 @@
FMT_BEGIN_NAMESPACE
// Check if std::chrono::local_t is available.
#ifndef FMT_USE_LOCAL_TIME
# ifdef __cpp_lib_chrono
# define FMT_USE_LOCAL_TIME (__cpp_lib_chrono >= 201907L)
# else
# define FMT_USE_LOCAL_TIME 0
# endif
#endif
// Check if std::chrono::utc_timestamp is available.
#ifndef FMT_USE_UTC_TIME
# ifdef __cpp_lib_chrono
@@ -453,6 +462,7 @@ auto write(OutputIt out, const std::tm& time, const std::locale& loc,
FMT_MODULE_EXPORT_BEGIN
#if FMT_USE_LOCAL_TIME
/**
Converts given time since epoch as ``std::time_t`` value into calendar time,
expressed in local time. Unlike ``std::localtime``, this function is
@@ -494,10 +504,12 @@ inline std::tm localtime(std::time_t time) {
return lt.tm_;
}
template<class Duration>
inline std::tm localtime(
std::chrono::time_point<std::chrono::system_clock> time_point) {
return localtime(std::chrono::system_clock::to_time_t(time_point));
std::chrono::local_time<Duration> time_point) {
return localtime(std::chrono::system_clock::to_time_t(std::chrono::current_zone()->to_sys(time_point)));
}
#endif
/**
Converts given time since epoch as ``std::time_t`` value into calendar time,
@@ -2103,6 +2115,37 @@ struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
auto format(std::chrono::time_point<std::chrono::system_clock, Duration> val,
FormatContext& ctx) const -> decltype(ctx.out()) {
using period = typename Duration::period;
if (period::num != 1 || period::den != 1 ||
std::is_floating_point<typename Duration::rep>::value) {
const auto epoch = val.time_since_epoch();
const auto subsecs = std::chrono::duration_cast<Duration>(
epoch - std::chrono::duration_cast<std::chrono::seconds>(epoch));
return formatter<std::tm, Char>::do_format(
gmtime(std::chrono::time_point_cast<std::chrono::seconds>(val)),
ctx, &subsecs);
}
return formatter<std::tm, Char>::format(
gmtime(std::chrono::time_point_cast<std::chrono::seconds>(val)),
ctx);
}
};
#if FMT_USE_LOCAL_TIME
template <typename Char, typename Duration>
struct formatter<std::chrono::local_time<Duration>,
Char> : formatter<std::tm, Char> {
FMT_CONSTEXPR formatter() {
basic_string_view<Char> default_specs =
detail::string_literal<Char, '%', 'F', ' ', '%', 'T'>{};
this->do_parse(default_specs.begin(), default_specs.end());
}
template <typename FormatContext>
auto format(std::chrono::local_time<Duration> val,
FormatContext& ctx) const -> decltype(ctx.out()) {
using period = typename Duration::period;
if (period::num != 1 || period::den != 1 ||
std::is_floating_point<typename Duration::rep>::value) {
const auto epoch = val.time_since_epoch();
@@ -2119,6 +2162,7 @@ struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
ctx);
}
};
#endif
#if FMT_USE_UTC_TIME
template <typename Char, typename Duration>