[PATCH 1/3] libstdc++: Use formatting locale for std::time_put formats

[PATCH 1/3] libstdc++: Use formatting locale for std::time_put formats

[Jonathan Wakely]

When using std::time_put to format a chrono value, we should imbue the
formatting locale into the stream. This ensures that when
std::time_put::do_put uses a ctype or __timepunct facet from the locale,
it gets the correct facets.

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (__formatter_chrono::_M_locale_fmt):
	Imbue locale into ostringstream.
---

This doesn't cause a problem with any existing formatters, but is needed
for the next patches in this series. I'll try to come up with a
standalone testcase that depends on this fix (involving a custom facet
derived from std::time_put which uses the locale in its do_put).

Tested x86_64-linux.

 libstdc++-v3/include/bits/chrono_io.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index c16b555df29..55ebd4ee061 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -1697,6 +1697,7 @@ namespace __format
 		      char __fmt, char __mod) const
 	{
 	  basic_ostringstream<_CharT> __os;
+	  __os.imbue(__loc);
 	  const auto& __tp = use_facet<time_put<_CharT>>(__loc);
 	  __tp.put(__os, __os, _S_space, &__tm, __fmt, __mod);
 	  if (__os)
-- 
2.48.1

[PATCH 2/3] libstdc++: Fix localized D_T_FMT %c formatting for <chrono> [PR117214]

[Jonathan Wakely]

From: XU Kailiang <xu2k3l4@outlook.com>

Formatting a time point with %c was implemented by calling
std::vprint_to with format string constructed from locale's D_T_FMT
string, but in some locales this string contains strftime specifiers
which are not valid for chrono-specs, e.g. %l. So just use _M_locale_fmt
to avoid this problem.

libstdc++-v3/ChangeLog:

	PR libstdc++/117214
	* include/bits/chrono_io.h (__formatter_chrono::_M_c): Use
	_M_locale_fmt to format %c time point.
	* testsuite/std/time/format/pr117214.cc: New test.

Signed-off-by: XU Kailiang <xu2k3l4@outlook.com>

Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
---

Tested x86_64-linux.

 libstdc++-v3/include/bits/chrono_io.h         | 35 ++++++++++---------
 .../testsuite/std/time/format/pr117214.cc     | 34 ++++++++++++++++++
 2 files changed, 53 insertions(+), 16 deletions(-)
 create mode 100644 libstdc++-v3/testsuite/std/time/format/pr117214.cc

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index 55ebd4ee061..86338d48d18 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -887,27 +887,30 @@ namespace __format
 
       template<typename _Tp, typename _FormatContext>
 	typename _FormatContext::iterator
-	_M_c(const _Tp& __tt, typename _FormatContext::iterator __out,
+	_M_c(const _Tp& __t, typename _FormatContext::iterator __out,
 	     _FormatContext& __ctx, bool __mod = false) const
 	{
 	  // %c  Locale's date and time representation.
 	  // %Ec Locale's alternate date and time representation.
 
-	  basic_string<_CharT> __fmt;
-	  auto __t = _S_floor_seconds(__tt);
-	  locale __loc = _M_locale(__ctx);
-	  const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
-	  const _CharT* __formats[2];
-	  __tp._M_date_time_formats(__formats);
-	  if (*__formats[__mod]) [[likely]]
-	    {
-	      __fmt = _GLIBCXX_WIDEN("{:L}");
-	      __fmt.insert(3u, __formats[__mod]);
-	    }
-	  else
-	    __fmt = _GLIBCXX_WIDEN("{:L%a %b %e %T %Y}");
-	  return std::vformat_to(std::move(__out), __loc, __fmt,
-				 std::make_format_args<_FormatContext>(__t));
+	  using namespace chrono;
+	  auto __d = _S_days(__t); // Either sys_days or local_days.
+	  using _TDays = decltype(__d);
+	  const year_month_day __ymd(__d);
+	  const auto __y = __ymd.year();
+	  const auto __hms = _S_hms(__t);
+
+	  struct tm __tm{};
+	  __tm.tm_year = (int)__y - 1900;
+	  __tm.tm_yday = (__d - _TDays(__y/January/1)).count();
+	  __tm.tm_mon = (unsigned)__ymd.month() - 1;
+	  __tm.tm_mday = (unsigned)__ymd.day();
+	  __tm.tm_wday = weekday(__d).c_encoding();
+	  __tm.tm_hour = __hms.hours().count();
+	  __tm.tm_min = __hms.minutes().count();
+	  __tm.tm_sec = __hms.seconds().count();
+	  return _M_locale_fmt(std::move(__out), _M_locale(__ctx), __tm, 'c',
+			       __mod ? 'E' : '\0');
 	}
 
       template<typename _Tp, typename _FormatContext>
diff --git a/libstdc++-v3/testsuite/std/time/format/pr117214.cc b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
new file mode 100644
index 00000000000..e7831832206
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
@@ -0,0 +1,34 @@
+// { dg-do run { target c++20 } }
+// { dg-require-namedlocale "aa_DJ.UTF-8" }
+// { dg-require-namedlocale "ar_SA.UTF-8" }
+// { dg-require-namedlocale "ca_AD.UTF-8" }
+// { dg-require-namedlocale "az_IR.UTF-8" }
+// { dg-require-namedlocale "my_MM.UTF-8" }
+
+#include <chrono>
+#include <locale>
+#include <testsuite_hooks.h>
+
+void
+test_c()
+{
+  const char *test_locales[] = {
+    "aa_DJ.UTF-8",
+    "ar_SA.UTF-8",
+    "ca_AD.UTF-8",
+    "az_IR.UTF-8",
+    "my_MM.UTF-8",
+  };
+  std::chrono::sys_seconds t{std::chrono::seconds{1}};
+
+  for (auto locale_name : test_locales)
+  {
+    auto s = std::format(std::locale(locale_name), "{:L%c}", t);
+    VERIFY( !s.empty() );
+  }
+}
+
+int main()
+{
+  test_c();
+}
-- 
2.48.1

[PATCH 3/3] libstdc++: Fix localized %c formatting for non-UTC times [PR117214]

[Jonathan Wakely]

The previous commit fixed most cases of %c formatting, but it
incorrectly prints times using the system's local time zone. This only
matters if the locale's %c format includes %Z, but some do.

To print a correct value for %Z we can set tm.tm_zone to either "UTC" or
the abbreviation passed to the formatter in the local-time-format-t
structure.

For local times with no info and for systems that don't support tm_zone
(which is new in POSIX.1-2024) we just set tm_isdst = -1 so that no zone
name is printed.

In theory, a locale's %c format could use %z which should print a +hhmm
offset from UTC. I'm unsure how to control that though. The new
tm_gmtoff field in combination with tm_isdst != -1 seems like it should
work, but using that without also setting tm_zone causes the system zone
to be used for %Z again. That means local_time_format(lt, nullptr, &off)
might work for a locale that uses %z but prints the wrong thing for %Z.
This commit doesn't set tm_gmtoff even if _M_offset_sec is provided for
a local-time-format-t value.

libstdc++-v3/ChangeLog:

	PR libstdc++/117214
	* configure.ac: Use AC_STRUCT_TIMEZONE.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* include/bits/chrono_io.h (__formatter_chrono::_M_c): Set
	tm_isdst and tm_zone.
	* testsuite/std/time/format/pr117214.cc: Check %c formatting of
	zoned_time and local time.
---

Tested x86_64-linux.

 libstdc++-v3/config.h.in                      |  18 ++
 libstdc++-v3/configure                        | 179 +++++++++++++++++-
 libstdc++-v3/configure.ac                     |   2 +
 libstdc++-v3/include/bits/chrono_io.h         |  32 +++-
 .../testsuite/std/time/format/pr117214.cc     |  65 +++++++
 5 files changed, 287 insertions(+), 9 deletions(-)

diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
index 91e920044ee..be151f43dd6 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -74,6 +74,10 @@
    don't. */
 #undef HAVE_DECL_STRNLEN
 
+/* Define to 1 if you have the declaration of `tzname', and to 0 if you don't.
+   */
+#undef HAVE_DECL_TZNAME
+
 /* Define to 1 if you have the <dirent.h> header file. */
 #undef HAVE_DIRENT_H
 
@@ -408,6 +412,9 @@
 /* Define to 1 if `d_type' is a member of `struct dirent'. */
 #undef HAVE_STRUCT_DIRENT_D_TYPE
 
+/* Define to 1 if `tm_zone' is a member of `struct tm'. */
+#undef HAVE_STRUCT_TM_TM_ZONE
+
 /* Define if strxfrm_l is available in <string.h>. */
 #undef HAVE_STRXFRM_L
 
@@ -499,9 +506,17 @@
 /* Define to 1 if the target supports thread-local storage. */
 #undef HAVE_TLS
 
+/* Define to 1 if your `struct tm' has `tm_zone'. Deprecated, use
+   `HAVE_STRUCT_TM_TM_ZONE' instead. */
+#undef HAVE_TM_ZONE
+
 /* Define if truncate is available in <unistd.h>. */
 #undef HAVE_TRUNCATE
 
+/* Define to 1 if you don't have `tm_zone' but do have the external array
+   `tzname'. */
+#undef HAVE_TZNAME
+
 /* Define to 1 if you have the <uchar.h> header file. */
 #undef HAVE_UCHAR_H
 
@@ -590,6 +605,9 @@
 /* Define to 1 if you have the ANSI C header files. */
 #undef STDC_HEADERS
 
+/* Define to 1 if your <sys/time.h> declares `struct tm'. */
+#undef TM_IN_SYS_TIME
+
 /* Version number of package */
 #undef VERSION
 
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 78758285f21..67d2b8c7b72 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -2731,6 +2731,63 @@ $as_echo "$ac_res" >&6; }
   eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
 
 } # ac_fn_c_check_decl
+
+# ac_fn_c_check_member LINENO AGGR MEMBER VAR INCLUDES
+# ----------------------------------------------------
+# Tries to find if the field MEMBER exists in type AGGR, after including
+# INCLUDES, setting cache variable VAR accordingly.
+ac_fn_c_check_member ()
+{
+  as_lineno=${as_lineno-"$1"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2.$3" >&5
+$as_echo_n "checking for $2.$3... " >&6; }
+if eval \${$4+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+$5
+int
+main ()
+{
+static $2 ac_aggr;
+if (ac_aggr.$3)
+return 0;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  eval "$4=yes"
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+$5
+int
+main ()
+{
+static $2 ac_aggr;
+if (sizeof ac_aggr.$3)
+return 0;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  eval "$4=yes"
+else
+  eval "$4=no"
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+eval ac_res=\$$4
+	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+  eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
+
+} # ac_fn_c_check_member
 cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
@@ -12280,7 +12337,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12283 "configure"
+#line 12340 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12386,7 +12443,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12389 "configure"
+#line 12446 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -16182,7 +16239,7 @@ $as_echo "$glibcxx_cv_atomic_long_long" >&6; }
   # Fake what AC_TRY_COMPILE does.
 
     cat > conftest.$ac_ext << EOF
-#line 16185 "configure"
+#line 16242 "configure"
 int main()
 {
   typedef bool atomic_type;
@@ -16217,7 +16274,7 @@ $as_echo "$glibcxx_cv_atomic_bool" >&6; }
     rm -f conftest*
 
     cat > conftest.$ac_ext << EOF
-#line 16220 "configure"
+#line 16277 "configure"
 int main()
 {
   typedef short atomic_type;
@@ -16252,7 +16309,7 @@ $as_echo "$glibcxx_cv_atomic_short" >&6; }
     rm -f conftest*
 
     cat > conftest.$ac_ext << EOF
-#line 16255 "configure"
+#line 16312 "configure"
 int main()
 {
   // NB: _Atomic_word not necessarily int.
@@ -16288,7 +16345,7 @@ $as_echo "$glibcxx_cv_atomic_int" >&6; }
     rm -f conftest*
 
     cat > conftest.$ac_ext << EOF
-#line 16291 "configure"
+#line 16348 "configure"
 int main()
 {
   typedef long long atomic_type;
@@ -16444,7 +16501,7 @@ $as_echo "mutex" >&6; }
   # unnecessary for this test.
 
     cat > conftest.$ac_ext << EOF
-#line 16447 "configure"
+#line 16504 "configure"
 int main()
 {
   _Decimal32 d1;
@@ -16486,7 +16543,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
   # unnecessary for this test.
 
   cat > conftest.$ac_ext << EOF
-#line 16489 "configure"
+#line 16546 "configure"
 template<typename T1, typename T2>
   struct same
   { typedef T2 type; };
@@ -54640,6 +54697,112 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether struct tm is in sys/time.h or time.h" >&5
+$as_echo_n "checking whether struct tm is in sys/time.h or time.h... " >&6; }
+if ${ac_cv_struct_tm+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <sys/types.h>
+#include <time.h>
+
+int
+main ()
+{
+struct tm tm;
+				     int *p = &tm.tm_sec;
+				     return !p;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  ac_cv_struct_tm=time.h
+else
+  ac_cv_struct_tm=sys/time.h
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_struct_tm" >&5
+$as_echo "$ac_cv_struct_tm" >&6; }
+if test $ac_cv_struct_tm = sys/time.h; then
+
+$as_echo "#define TM_IN_SYS_TIME 1" >>confdefs.h
+
+fi
+
+ac_fn_c_check_member "$LINENO" "struct tm" "tm_zone" "ac_cv_member_struct_tm_tm_zone" "#include <sys/types.h>
+#include <$ac_cv_struct_tm>
+
+"
+if test "x$ac_cv_member_struct_tm_tm_zone" = xyes; then :
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_STRUCT_TM_TM_ZONE 1
+_ACEOF
+
+
+fi
+
+if test "$ac_cv_member_struct_tm_tm_zone" = yes; then
+
+$as_echo "#define HAVE_TM_ZONE 1" >>confdefs.h
+
+else
+  ac_fn_c_check_decl "$LINENO" "tzname" "ac_cv_have_decl_tzname" "#include <time.h>
+"
+if test "x$ac_cv_have_decl_tzname" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_TZNAME $ac_have_decl
+_ACEOF
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for tzname" >&5
+$as_echo_n "checking for tzname... " >&6; }
+if ${ac_cv_var_tzname+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test x$gcc_no_link = xyes; then
+  as_fn_error $? "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5
+fi
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <time.h>
+#if !HAVE_DECL_TZNAME
+extern char *tzname[];
+#endif
+
+int
+main ()
+{
+return tzname[0][0];
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  ac_cv_var_tzname=yes
+else
+  ac_cv_var_tzname=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_var_tzname" >&5
+$as_echo "$ac_cv_var_tzname" >&6; }
+  if test $ac_cv_var_tzname = yes; then
+
+$as_echo "#define HAVE_TZNAME 1" >>confdefs.h
+
+  fi
+fi
+
+
 # Define documentation rules conditionally.
 
 # See if makeinfo has been installed and is modern enough
diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index a3b257fe652..fe0cdde1f7a 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -584,6 +584,8 @@ GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES
 # For std::text_encoding
 GLIBCXX_CHECK_TEXT_ENCODING
 
+AC_STRUCT_TIMEZONE
+
 # Define documentation rules conditionally.
 
 # See if makeinfo has been installed and is modern enough
diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index 86338d48d18..08969166d2f 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -894,13 +894,42 @@ namespace __format
 	  // %Ec Locale's alternate date and time representation.
 
 	  using namespace chrono;
+	  using ::std::chrono::__detail::__utc_leap_second;
+	  using ::std::chrono::__detail::__local_time_fmt;
+
+	  struct tm __tm{};
+
+	  // Some locales use %Z in their %c format but we don't want strftime
+	  // to use the system's local time zone (from /etc/localtime or $TZ)
+	  // as the output for %Z. Setting tm_isdst to -1 says there is no
+	  // time zone info available for the time in __tm.
+	  __tm.tm_isdst = -1;
+
+#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
+	  // POSIX.1-2024 adds tm.tm_zone which will be used for %Z.
+	  if constexpr (__is_time_point_v<_Tp>)
+	    {
+	      // One of sys_time, utc_time, or local_time.
+	      if constexpr (!is_same_v<typename _Tp::clock, local_t>)
+		__tm.tm_zone = "UTC";
+	    }
+	  else if constexpr (__is_specialization_of<_Tp, __local_time_fmt>)
+	    {
+	      // local-time-format-t is used to provide time zone info for
+	      // one of zoned_time, tai_time, gps_time, or local_time.
+	      if (__t._M_abbrev)
+		__tm.tm_zone = __t._M_abbrev->c_str();
+	    }
+	  else
+	    __tm.tm_zone = "UTC";
+#endif
+
 	  auto __d = _S_days(__t); // Either sys_days or local_days.
 	  using _TDays = decltype(__d);
 	  const year_month_day __ymd(__d);
 	  const auto __y = __ymd.year();
 	  const auto __hms = _S_hms(__t);
 
-	  struct tm __tm{};
 	  __tm.tm_year = (int)__y - 1900;
 	  __tm.tm_yday = (__d - _TDays(__y/January/1)).count();
 	  __tm.tm_mon = (unsigned)__ymd.month() - 1;
@@ -909,6 +938,7 @@ namespace __format
 	  __tm.tm_hour = __hms.hours().count();
 	  __tm.tm_min = __hms.minutes().count();
 	  __tm.tm_sec = __hms.seconds().count();
+
 	  return _M_locale_fmt(std::move(__out), _M_locale(__ctx), __tm, 'c',
 			       __mod ? 'E' : '\0');
 	}
diff --git a/libstdc++-v3/testsuite/std/time/format/pr117214.cc b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
index e7831832206..87c703dd255 100644
--- a/libstdc++-v3/testsuite/std/time/format/pr117214.cc
+++ b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
@@ -28,7 +28,72 @@ test_c()
   }
 }
 
+#include <stdlib.h>
+#include <time.h>
+
+extern "C++" int tzset(int);
+
+template<typename T = void>
+void maybe_set_tz()
+{
+#ifdef _GLIBCXX_HAVE_SETENV
+  // True if a function 'T tzset()' has been declared.
+  if constexpr (requires (T (*p)()) { p = &tzset; })
+  {
+    setenv("TZ", "GMT0", 1);
+    tzset(); // Set C library's global time zone to GMT0
+  }
+#endif
+}
+
+void
+test_c_zoned()
+{
+#if _GLIBCXX_USE_CXX11_ABI
+  maybe_set_tz();
+
+  using namespace std::chrono;
+  auto time = sys_days(2025y/March/19) + 15h;
+  zoned_time z("America/New_York", time);
+  auto s = std::format(std::locale("aa_DJ.UTF-8"), "{:L%c}", z);
+  VERIFY( s.find("11:00") != s.npos );
+
+  // We should not print an incorrect time zone.
+  VERIFY( s.find("GMT") == s.npos );
+  VERIFY( s.find("UTC") == s.npos );
+
+#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
+  // When tm.tm_zone is supported, we do print the correct time zone.
+  VERIFY( s.find(z.get_info().abbrev) != s.npos );
+#endif
+#endif
+}
+
+void
+test_c_local()
+{
+  maybe_set_tz();
+
+  std::locale("aa_DJ.UTF-8");
+  using namespace std::chrono;
+  auto time = local_days(2025y/March/19) + 11h;
+  auto s = std::format(std::locale("aa_DJ.UTF-8"), "{:L%c}", time);
+  // __builtin_printf("%s\n", s.c_str()); return;
+  VERIFY( s.find("11:00") != s.npos );
+
+  // We should not print any time zone.
+  VERIFY( s.find("GMT") == s.npos );
+  VERIFY( s.find("UTC") == s.npos );
+
+#if _GLIBCXX_USE_CXX11_ABI
+  zoned_time z(system_clock::now());
+  VERIFY( s.find(z.get_info().abbrev) == s.npos );
+#endif
+}
+
 int main()
 {
   test_c();
+  test_c_zoned();
+  test_c_local();
 }
-- 
2.48.1

[PATCH v2 1/3] libstdc++: Use formatting locale for std::time_put formats

[Jonathan Wakely]

When using std::time_put to format a chrono value, we should imbue the
formatting locale into the stream. This ensures that when
std::time_put::do_put uses a ctype or __timepunct facet from the locale,
it gets the correct facets.

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (__formatter_chrono::_M_locale_fmt):
	Imbue locale into ostringstream.
	* testsuite/std/time/format/localized.cc: Check that correct
	locale is used for call to time_put::put.
---

Now with a test that shows the bug independent of the PR117214 patches
to use std::time_put for %c formats.

Tested x86_64-linux.

 libstdc++-v3/include/bits/chrono_io.h         |  1 +
 .../testsuite/std/time/format/localized.cc    | 30 +++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index c16b555df29..55ebd4ee061 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -1697,6 +1697,7 @@ namespace __format
 		      char __fmt, char __mod) const
 	{
 	  basic_ostringstream<_CharT> __os;
+	  __os.imbue(__loc);
 	  const auto& __tp = use_facet<time_put<_CharT>>(__loc);
 	  __tp.put(__os, __os, _S_space, &__tm, __fmt, __mod);
 	  if (__os)
diff --git a/libstdc++-v3/testsuite/std/time/format/localized.cc b/libstdc++-v3/testsuite/std/time/format/localized.cc
index 393d0d200e4..437a4a011b2 100644
--- a/libstdc++-v3/testsuite/std/time/format/localized.cc
+++ b/libstdc++-v3/testsuite/std/time/format/localized.cc
@@ -13,6 +13,7 @@
 
 #include <chrono>
 #include <format>
+#include <locale>
 #include <stdio.h>
 #include <testsuite_hooks.h>
 
@@ -81,6 +82,35 @@ test_en()
     }
 }
 
+void
+test_locale_imbued()
+{
+  // Custom time_put facet which returns %b string for %Om
+  struct TimePut : std::time_put<char>
+  {
+    iter_type
+    do_put(iter_type out, std::ios_base& io, char_type fill, const tm* t,
+	   char format, char modifier) const override
+    {
+      if (format == 'm' && modifier == 'O')
+	format = 'b';
+      return std::time_put<char>::do_put(out, io, fill, t, format, 0);
+    }
+  };
+
+  auto m = std::chrono::March;
+
+  std::locale fr(ISO_8859(1,fr_FR));
+  std::locale fr2(fr, new TimePut);
+  auto s1 = std::format(fr2, "{:L%Om}", m);
+  VERIFY( s1 == std::format(fr, "{:L}", m) );
+
+  std::locale es(ISO_8859(1,es_ES));
+  std::locale es2(es, new TimePut);
+  auto s2 = std::format(es2, "{:L%Om}", m);
+  VERIFY( s2 == std::format(es, "{:L}", m) );
+}
+
 int main()
 {
   test_ru();
-- 
2.49.0

Re: [PATCH v2 1/3] libstdc++: Use formatting locale for std::time_put formats

[Jonathan Wakely]

On Thu, 20 Mar 2025 at 16:16, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> When using std::time_put to format a chrono value, we should imbue the
> formatting locale into the stream. This ensures that when
> std::time_put::do_put uses a ctype or __timepunct facet from the locale,
> it gets the correct facets.
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/chrono_io.h (__formatter_chrono::_M_locale_fmt):
>         Imbue locale into ostringstream.
>         * testsuite/std/time/format/localized.cc: Check that correct
>         locale is used for call to time_put::put.
> ---
>
> Now with a test that shows the bug independent of the PR117214 patches
> to use std::time_put for %c formats.
>
> Tested x86_64-linux.
>
>  libstdc++-v3/include/bits/chrono_io.h         |  1 +
>  .../testsuite/std/time/format/localized.cc    | 30 +++++++++++++++++++
>  2 files changed, 31 insertions(+)
>
> diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
> index c16b555df29..55ebd4ee061 100644
> --- a/libstdc++-v3/include/bits/chrono_io.h
> +++ b/libstdc++-v3/include/bits/chrono_io.h
> @@ -1697,6 +1697,7 @@ namespace __format
>                       char __fmt, char __mod) const
>         {
>           basic_ostringstream<_CharT> __os;
> +         __os.imbue(__loc);
>           const auto& __tp = use_facet<time_put<_CharT>>(__loc);
>           __tp.put(__os, __os, _S_space, &__tm, __fmt, __mod);
>           if (__os)
> diff --git a/libstdc++-v3/testsuite/std/time/format/localized.cc b/libstdc++-v3/testsuite/std/time/format/localized.cc
> index 393d0d200e4..437a4a011b2 100644
> --- a/libstdc++-v3/testsuite/std/time/format/localized.cc
> +++ b/libstdc++-v3/testsuite/std/time/format/localized.cc
> @@ -13,6 +13,7 @@
>
>  #include <chrono>
>  #include <format>
> +#include <locale>
>  #include <stdio.h>
>  #include <testsuite_hooks.h>
>
> @@ -81,6 +82,35 @@ test_en()
>      }
>  }
>
> +void
> +test_locale_imbued()
> +{
> +  // Custom time_put facet which returns %b string for %Om
> +  struct TimePut : std::time_put<char>
> +  {
> +    iter_type
> +    do_put(iter_type out, std::ios_base& io, char_type fill, const tm* t,
> +          char format, char modifier) const override
> +    {
> +      if (format == 'm' && modifier == 'O')
> +       format = 'b';
> +      return std::time_put<char>::do_put(out, io, fill, t, format, 0);
> +    }
> +  };
> +
> +  auto m = std::chrono::March;
> +
> +  std::locale fr(ISO_8859(1,fr_FR));
> +  std::locale fr2(fr, new TimePut);
> +  auto s1 = std::format(fr2, "{:L%Om}", m);
> +  VERIFY( s1 == std::format(fr, "{:L}", m) );
> +
> +  std::locale es(ISO_8859(1,es_ES));
> +  std::locale es2(es, new TimePut);
> +  auto s2 = std::format(es2, "{:L%Om}", m);
> +  VERIFY( s2 == std::format(es, "{:L}", m) );
> +}
> +
>  int main()
>  {
>    test_ru();

It would help if I added the new test_locale_imbued() function to main
so that it actually runs.

Luckily it passes when I do that.

Re: [PATCH v2 1/3] libstdc++: Use formatting locale for std::time_put formats

[Tomasz Kaminski]

[-- Attachment #1: Type: text/plain, Size: 3368 bytes --]

On Thu, Mar 20, 2025 at 5:29 PM Jonathan Wakely <jwakely@redhat.com> wrote:

> On Thu, 20 Mar 2025 at 16:16, Jonathan Wakely <jwakely@redhat.com> wrote:
> >
> > When using std::time_put to format a chrono value, we should imbue the
> > formatting locale into the stream. This ensures that when
> > std::time_put::do_put uses a ctype or __timepunct facet from the locale,
> > it gets the correct facets.
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * include/bits/chrono_io.h (__formatter_chrono::_M_locale_fmt):
> >         Imbue locale into ostringstream.
> >         * testsuite/std/time/format/localized.cc: Check that correct
> >         locale is used for call to time_put::put.
> > ---
> >
> > Now with a test that shows the bug independent of the PR117214 patches
> > to use std::time_put for %c formats.
> >
> > Tested x86_64-linux.
> >
> >  libstdc++-v3/include/bits/chrono_io.h         |  1 +
> >  .../testsuite/std/time/format/localized.cc    | 30 +++++++++++++++++++
> >  2 files changed, 31 insertions(+)
> >
> > diff --git a/libstdc++-v3/include/bits/chrono_io.h
> b/libstdc++-v3/include/bits/chrono_io.h
> > index c16b555df29..55ebd4ee061 100644
> > --- a/libstdc++-v3/include/bits/chrono_io.h
> > +++ b/libstdc++-v3/include/bits/chrono_io.h
> > @@ -1697,6 +1697,7 @@ namespace __format
> >                       char __fmt, char __mod) const
> >         {
> >           basic_ostringstream<_CharT> __os;
> > +         __os.imbue(__loc);
> >           const auto& __tp = use_facet<time_put<_CharT>>(__loc);
> >           __tp.put(__os, __os, _S_space, &__tm, __fmt, __mod);
> >           if (__os)
> > diff --git a/libstdc++-v3/testsuite/std/time/format/localized.cc
> b/libstdc++-v3/testsuite/std/time/format/localized.cc
> > index 393d0d200e4..437a4a011b2 100644
> > --- a/libstdc++-v3/testsuite/std/time/format/localized.cc
> > +++ b/libstdc++-v3/testsuite/std/time/format/localized.cc
> > @@ -13,6 +13,7 @@
> >
> >  #include <chrono>
> >  #include <format>
> > +#include <locale>
> >  #include <stdio.h>
> >  #include <testsuite_hooks.h>
> >
> > @@ -81,6 +82,35 @@ test_en()
> >      }
> >  }
> >
> > +void
> > +test_locale_imbued()
> > +{
> > +  // Custom time_put facet which returns %b string for %Om
> > +  struct TimePut : std::time_put<char>
> > +  {
> > +    iter_type
> > +    do_put(iter_type out, std::ios_base& io, char_type fill, const tm*
> t,
> > +          char format, char modifier) const override
> > +    {
> > +      if (format == 'm' && modifier == 'O')
> > +       format = 'b';
> > +      return std::time_put<char>::do_put(out, io, fill, t, format, 0);
> > +    }
> > +  };
> > +
> > +  auto m = std::chrono::March;
> > +
> > +  std::locale fr(ISO_8859(1,fr_FR));
> > +  std::locale fr2(fr, new TimePut);
> > +  auto s1 = std::format(fr2, "{:L%Om}", m);
> > +  VERIFY( s1 == std::format(fr, "{:L}", m) );
> > +
> > +  std::locale es(ISO_8859(1,es_ES));
> > +  std::locale es2(es, new TimePut);
> > +  auto s2 = std::format(es2, "{:L%Om}", m);
> > +  VERIFY( s2 == std::format(es, "{:L}", m) );
> > +}
> > +
> >  int main()
> >  {
> >    test_ru();
>
> It would help if I added the new test_locale_imbued() function to main
> so that it actually runs.
>
LGTM with that addition.

>
> Luckily it passes when I do that.
>
>

Re: [PATCH 2/3] libstdc++: Fix localized D_T_FMT %c formatting for <chrono> [PR117214]

[Tomasz Kaminski]

[-- Attachment #1: Type: text/plain, Size: 4639 bytes --]

On Thu, Mar 20, 2025 at 10:31 AM Jonathan Wakely <jwakely@redhat.com> wrote:

> From: XU Kailiang <xu2k3l4@outlook.com>
>
> Formatting a time point with %c was implemented by calling
> std::vprint_to with format string constructed from locale's D_T_FMT
> string, but in some locales this string contains strftime specifiers
> which are not valid for chrono-specs, e.g. %l. So just use _M_locale_fmt
> to avoid this problem.
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/117214
>         * include/bits/chrono_io.h (__formatter_chrono::_M_c): Use
>         _M_locale_fmt to format %c time point.
>         * testsuite/std/time/format/pr117214.cc: New test.
>
> Signed-off-by: XU Kailiang <xu2k3l4@outlook.com>
>
> Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
> ---
>
> Tested x86_64-linux.
>
LGTM

>
>  libstdc++-v3/include/bits/chrono_io.h         | 35 ++++++++++---------
>  .../testsuite/std/time/format/pr117214.cc     | 34 ++++++++++++++++++
>  2 files changed, 53 insertions(+), 16 deletions(-)
>  create mode 100644 libstdc++-v3/testsuite/std/time/format/pr117214.cc
>
> diff --git a/libstdc++-v3/include/bits/chrono_io.h
> b/libstdc++-v3/include/bits/chrono_io.h
> index 55ebd4ee061..86338d48d18 100644
> --- a/libstdc++-v3/include/bits/chrono_io.h
> +++ b/libstdc++-v3/include/bits/chrono_io.h
> @@ -887,27 +887,30 @@ namespace __format
>
>        template<typename _Tp, typename _FormatContext>
>         typename _FormatContext::iterator
> -       _M_c(const _Tp& __tt, typename _FormatContext::iterator __out,
> +       _M_c(const _Tp& __t, typename _FormatContext::iterator __out,
>              _FormatContext& __ctx, bool __mod = false) const
>         {
>           // %c  Locale's date and time representation.
>           // %Ec Locale's alternate date and time representation.
>
> -         basic_string<_CharT> __fmt;
> -         auto __t = _S_floor_seconds(__tt);
> -         locale __loc = _M_locale(__ctx);
> -         const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
> -         const _CharT* __formats[2];
> -         __tp._M_date_time_formats(__formats);
> -         if (*__formats[__mod]) [[likely]]
> -           {
> -             __fmt = _GLIBCXX_WIDEN("{:L}");
> -             __fmt.insert(3u, __formats[__mod]);
> -           }
> -         else
> -           __fmt = _GLIBCXX_WIDEN("{:L%a %b %e %T %Y}");
> -         return std::vformat_to(std::move(__out), __loc, __fmt,
> -
> std::make_format_args<_FormatContext>(__t));
> +         using namespace chrono;
> +         auto __d = _S_days(__t); // Either sys_days or local_days.
> +         using _TDays = decltype(__d);
> +         const year_month_day __ymd(__d);
> +         const auto __y = __ymd.year();
> +         const auto __hms = _S_hms(__t);
> +
> +         struct tm __tm{};
> +         __tm.tm_year = (int)__y - 1900;
> +         __tm.tm_yday = (__d - _TDays(__y/January/1)).count();
> +         __tm.tm_mon = (unsigned)__ymd.month() - 1;
> +         __tm.tm_mday = (unsigned)__ymd.day();
> +         __tm.tm_wday = weekday(__d).c_encoding();
> +         __tm.tm_hour = __hms.hours().count();
> +         __tm.tm_min = __hms.minutes().count();
> +         __tm.tm_sec = __hms.seconds().count();
> +         return _M_locale_fmt(std::move(__out), _M_locale(__ctx), __tm,
> 'c',
> +                              __mod ? 'E' : '\0');
>         }
>
>        template<typename _Tp, typename _FormatContext>
> diff --git a/libstdc++-v3/testsuite/std/time/format/pr117214.cc
> b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
> new file mode 100644
> index 00000000000..e7831832206
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
> @@ -0,0 +1,34 @@
> +// { dg-do run { target c++20 } }
> +// { dg-require-namedlocale "aa_DJ.UTF-8" }
> +// { dg-require-namedlocale "ar_SA.UTF-8" }
> +// { dg-require-namedlocale "ca_AD.UTF-8" }
> +// { dg-require-namedlocale "az_IR.UTF-8" }
> +// { dg-require-namedlocale "my_MM.UTF-8" }
> +
> +#include <chrono>
> +#include <locale>
> +#include <testsuite_hooks.h>
> +
> +void
> +test_c()
> +{
> +  const char *test_locales[] = {
> +    "aa_DJ.UTF-8",
> +    "ar_SA.UTF-8",
> +    "ca_AD.UTF-8",
> +    "az_IR.UTF-8",
> +    "my_MM.UTF-8",
> +  };
> +  std::chrono::sys_seconds t{std::chrono::seconds{1}};
> +
> +  for (auto locale_name : test_locales)
> +  {
> +    auto s = std::format(std::locale(locale_name), "{:L%c}", t);
> +    VERIFY( !s.empty() );
> +  }
> +}
> +
> +int main()
> +{
> +  test_c();
> +}
> --
> 2.48.1
>
>

Re: [PATCH v2 1/3] libstdc++: Use formatting locale for std::time_put formats

[Jonathan Wakely]

On Fri, 21 Mar 2025 at 09:47, Tomasz Kaminski <tkaminsk@redhat.com> wrote:
>
>
>
> On Thu, Mar 20, 2025 at 5:29 PM Jonathan Wakely <jwakely@redhat.com> wrote:
>>
>> On Thu, 20 Mar 2025 at 16:16, Jonathan Wakely <jwakely@redhat.com> wrote:
>> >
>> > When using std::time_put to format a chrono value, we should imbue the
>> > formatting locale into the stream. This ensures that when
>> > std::time_put::do_put uses a ctype or __timepunct facet from the locale,
>> > it gets the correct facets.
>> >
>> > libstdc++-v3/ChangeLog:
>> >
>> >         * include/bits/chrono_io.h (__formatter_chrono::_M_locale_fmt):
>> >         Imbue locale into ostringstream.
>> >         * testsuite/std/time/format/localized.cc: Check that correct
>> >         locale is used for call to time_put::put.
>> > ---
>> >
>> > Now with a test that shows the bug independent of the PR117214 patches
>> > to use std::time_put for %c formats.
>> >
>> > Tested x86_64-linux.
>> >
>> >  libstdc++-v3/include/bits/chrono_io.h         |  1 +
>> >  .../testsuite/std/time/format/localized.cc    | 30 +++++++++++++++++++
>> >  2 files changed, 31 insertions(+)
>> >
>> > diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
>> > index c16b555df29..55ebd4ee061 100644
>> > --- a/libstdc++-v3/include/bits/chrono_io.h
>> > +++ b/libstdc++-v3/include/bits/chrono_io.h
>> > @@ -1697,6 +1697,7 @@ namespace __format
>> >                       char __fmt, char __mod) const
>> >         {
>> >           basic_ostringstream<_CharT> __os;
>> > +         __os.imbue(__loc);
>> >           const auto& __tp = use_facet<time_put<_CharT>>(__loc);
>> >           __tp.put(__os, __os, _S_space, &__tm, __fmt, __mod);
>> >           if (__os)
>> > diff --git a/libstdc++-v3/testsuite/std/time/format/localized.cc b/libstdc++-v3/testsuite/std/time/format/localized.cc
>> > index 393d0d200e4..437a4a011b2 100644
>> > --- a/libstdc++-v3/testsuite/std/time/format/localized.cc
>> > +++ b/libstdc++-v3/testsuite/std/time/format/localized.cc
>> > @@ -13,6 +13,7 @@
>> >
>> >  #include <chrono>
>> >  #include <format>
>> > +#include <locale>
>> >  #include <stdio.h>
>> >  #include <testsuite_hooks.h>
>> >
>> > @@ -81,6 +82,35 @@ test_en()
>> >      }
>> >  }
>> >
>> > +void
>> > +test_locale_imbued()
>> > +{
>> > +  // Custom time_put facet which returns %b string for %Om
>> > +  struct TimePut : std::time_put<char>
>> > +  {
>> > +    iter_type
>> > +    do_put(iter_type out, std::ios_base& io, char_type fill, const tm* t,
>> > +          char format, char modifier) const override
>> > +    {
>> > +      if (format == 'm' && modifier == 'O')
>> > +       format = 'b';
>> > +      return std::time_put<char>::do_put(out, io, fill, t, format, 0);
>> > +    }
>> > +  };
>> > +
>> > +  auto m = std::chrono::March;
>> > +
>> > +  std::locale fr(ISO_8859(1,fr_FR));
>> > +  std::locale fr2(fr, new TimePut);
>> > +  auto s1 = std::format(fr2, "{:L%Om}", m);
>> > +  VERIFY( s1 == std::format(fr, "{:L}", m) );
>> > +
>> > +  std::locale es(ISO_8859(1,es_ES));
>> > +  std::locale es2(es, new TimePut);
>> > +  auto s2 = std::format(es2, "{:L%Om}", m);
>> > +  VERIFY( s2 == std::format(es, "{:L}", m) );
>> > +}
>> > +
>> >  int main()
>> >  {
>> >    test_ru();
>>
>> It would help if I added the new test_locale_imbued() function to main
>> so that it actually runs.
>
> LGTM with that addition.

I also added some more comments in the new test, to explain what is
expected (so it's more clear why it didn't work before the commit).


>>
>>
>> Luckily it passes when I do that.
>>

Re: [PATCH 3/3] libstdc++: Fix localized %c formatting for non-UTC times [PR117214]

[Tomasz Kaminski]

[-- Attachment #1: Type: text/plain, Size: 16209 bytes --]

On Thu, Mar 20, 2025 at 10:39 AM Jonathan Wakely <jwakely@redhat.com> wrote:

> The previous commit fixed most cases of %c formatting, but it
> incorrectly prints times using the system's local time zone. This only
> matters if the locale's %c format includes %Z, but some do.
>
> To print a correct value for %Z we can set tm.tm_zone to either "UTC" or
> the abbreviation passed to the formatter in the local-time-format-t
> structure.
>
> For local times with no info and for systems that don't support tm_zone
> (which is new in POSIX.1-2024) we just set tm_isdst = -1 so that no zone
> name is printed.
>
> In theory, a locale's %c format could use %z which should print a +hhmm
> offset from UTC. I'm unsure how to control that though. The new
> tm_gmtoff field in combination with tm_isdst != -1 seems like it should
> work, but using that without also setting tm_zone causes the system zone
> to be used for %Z again. That means local_time_format(lt, nullptr, &off)
> might work for a locale that uses %z but prints the wrong thing for %Z.
> This commit doesn't set tm_gmtoff even if _M_offset_sec is provided for
> a local-time-format-t value.
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/117214
>         * configure.ac: Use AC_STRUCT_TIMEZONE.
>         * config.h.in: Regenerate.
>         * configure: Regenerate.
>         * include/bits/chrono_io.h (__formatter_chrono::_M_c): Set
>         tm_isdst and tm_zone.
>         * testsuite/std/time/format/pr117214.cc: Check %c formatting of
>         zoned_time and local time.
> ---
>
> Tested x86_64-linux.
>
The c++ code parts LGTM, however the changes in config.h.in and
configure went over my head: they seem to check for new members,
but I cannot confirm if they are correct and according to best practices.

>
>  libstdc++-v3/config.h.in                      |  18 ++
>  libstdc++-v3/configure                        | 179 +++++++++++++++++-
>  libstdc++-v3/configure.ac                     |   2 +
>  libstdc++-v3/include/bits/chrono_io.h         |  32 +++-
>  .../testsuite/std/time/format/pr117214.cc     |  65 +++++++
>  5 files changed, 287 insertions(+), 9 deletions(-)
>
> diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
> index 91e920044ee..be151f43dd6 100644
> --- a/libstdc++-v3/config.h.in
> +++ b/libstdc++-v3/config.h.in
> @@ -74,6 +74,10 @@
>     don't. */
>  #undef HAVE_DECL_STRNLEN
>
> +/* Define to 1 if you have the declaration of `tzname', and to 0 if you
> don't.
> +   */
> +#undef HAVE_DECL_TZNAME
> +
>  /* Define to 1 if you have the <dirent.h> header file. */
>  #undef HAVE_DIRENT_H
>
> @@ -408,6 +412,9 @@
>  /* Define to 1 if `d_type' is a member of `struct dirent'. */
>  #undef HAVE_STRUCT_DIRENT_D_TYPE
>
> +/* Define to 1 if `tm_zone' is a member of `struct tm'. */
> +#undef HAVE_STRUCT_TM_TM_ZONE
> +
>  /* Define if strxfrm_l is available in <string.h>. */
>  #undef HAVE_STRXFRM_L
>
> @@ -499,9 +506,17 @@
>  /* Define to 1 if the target supports thread-local storage. */
>  #undef HAVE_TLS
>
> +/* Define to 1 if your `struct tm' has `tm_zone'. Deprecated, use
> +   `HAVE_STRUCT_TM_TM_ZONE' instead. */
> +#undef HAVE_TM_ZONE
> +
>  /* Define if truncate is available in <unistd.h>. */
>  #undef HAVE_TRUNCATE
>
> +/* Define to 1 if you don't have `tm_zone' but do have the external array
> +   `tzname'. */
> +#undef HAVE_TZNAME
> +
>  /* Define to 1 if you have the <uchar.h> header file. */
>  #undef HAVE_UCHAR_H
>
> @@ -590,6 +605,9 @@
>  /* Define to 1 if you have the ANSI C header files. */
>  #undef STDC_HEADERS
>
> +/* Define to 1 if your <sys/time.h> declares `struct tm'. */
> +#undef TM_IN_SYS_TIME
> +
>  /* Version number of package */
>  #undef VERSION
>
> diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
> index 78758285f21..67d2b8c7b72 100755
> --- a/libstdc++-v3/configure
> +++ b/libstdc++-v3/configure
> @@ -2731,6 +2731,63 @@ $as_echo "$ac_res" >&6; }
>    eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
>
>  } # ac_fn_c_check_decl
> +
> +# ac_fn_c_check_member LINENO AGGR MEMBER VAR INCLUDES
> +# ----------------------------------------------------
> +# Tries to find if the field MEMBER exists in type AGGR, after including
> +# INCLUDES, setting cache variable VAR accordingly.
> +ac_fn_c_check_member ()
> +{
> +  as_lineno=${as_lineno-"$1"}
> as_lineno_stack=as_lineno_stack=$as_lineno_stack
> +  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2.$3" >&5
> +$as_echo_n "checking for $2.$3... " >&6; }
> +if eval \${$4+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +/* end confdefs.h.  */
> +$5
> +int
> +main ()
> +{
> +static $2 ac_aggr;
> +if (ac_aggr.$3)
> +return 0;
> +  ;
> +  return 0;
> +}
> +_ACEOF
> +if ac_fn_c_try_compile "$LINENO"; then :
> +  eval "$4=yes"
> +else
> +  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +/* end confdefs.h.  */
> +$5
> +int
> +main ()
> +{
> +static $2 ac_aggr;
> +if (sizeof ac_aggr.$3)
> +return 0;
> +  ;
> +  return 0;
> +}
> +_ACEOF
> +if ac_fn_c_try_compile "$LINENO"; then :
> +  eval "$4=yes"
> +else
> +  eval "$4=no"
> +fi
> +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
> +fi
> +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
> +fi
> +eval ac_res=\$$4
> +              { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res"
> >&5
> +$as_echo "$ac_res" >&6; }
> +  eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
> +
> +} # ac_fn_c_check_member
>  cat >config.log <<_ACEOF
>  This file contains any messages produced by compilers while
>  running configure, to aid debugging if configure makes a mistake.
> @@ -12280,7 +12337,7 @@ else
>    lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
>    lt_status=$lt_dlunknown
>    cat > conftest.$ac_ext <<_LT_EOF
> -#line 12283 "configure"
> +#line 12340 "configure"
>  #include "confdefs.h"
>
>  #if HAVE_DLFCN_H
> @@ -12386,7 +12443,7 @@ else
>    lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
>    lt_status=$lt_dlunknown
>    cat > conftest.$ac_ext <<_LT_EOF
> -#line 12389 "configure"
> +#line 12446 "configure"
>  #include "confdefs.h"
>
>  #if HAVE_DLFCN_H
> @@ -16182,7 +16239,7 @@ $as_echo "$glibcxx_cv_atomic_long_long" >&6; }
>    # Fake what AC_TRY_COMPILE does.
>
>      cat > conftest.$ac_ext << EOF
> -#line 16185 "configure"
> +#line 16242 "configure"
>  int main()
>  {
>    typedef bool atomic_type;
> @@ -16217,7 +16274,7 @@ $as_echo "$glibcxx_cv_atomic_bool" >&6; }
>      rm -f conftest*
>
>      cat > conftest.$ac_ext << EOF
> -#line 16220 "configure"
> +#line 16277 "configure"
>  int main()
>  {
>    typedef short atomic_type;
> @@ -16252,7 +16309,7 @@ $as_echo "$glibcxx_cv_atomic_short" >&6; }
>      rm -f conftest*
>
>      cat > conftest.$ac_ext << EOF
> -#line 16255 "configure"
> +#line 16312 "configure"
>  int main()
>  {
>    // NB: _Atomic_word not necessarily int.
> @@ -16288,7 +16345,7 @@ $as_echo "$glibcxx_cv_atomic_int" >&6; }
>      rm -f conftest*
>
>      cat > conftest.$ac_ext << EOF
> -#line 16291 "configure"
> +#line 16348 "configure"
>  int main()
>  {
>    typedef long long atomic_type;
> @@ -16444,7 +16501,7 @@ $as_echo "mutex" >&6; }
>    # unnecessary for this test.
>
>      cat > conftest.$ac_ext << EOF
> -#line 16447 "configure"
> +#line 16504 "configure"
>  int main()
>  {
>    _Decimal32 d1;
> @@ -16486,7 +16543,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
>    # unnecessary for this test.
>
>    cat > conftest.$ac_ext << EOF
> -#line 16489 "configure"
> +#line 16546 "configure"
>  template<typename T1, typename T2>
>    struct same
>    { typedef T2 type; };
> @@ -54640,6 +54697,112 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
>
>
>
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether struct tm is in
> sys/time.h or time.h" >&5
> +$as_echo_n "checking whether struct tm is in sys/time.h or time.h... "
> >&6; }
> +if ${ac_cv_struct_tm+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +/* end confdefs.h.  */
> +#include <sys/types.h>
> +#include <time.h>
> +
> +int
> +main ()
> +{
> +struct tm tm;
> +                                    int *p = &tm.tm_sec;
> +                                    return !p;
> +  ;
> +  return 0;
> +}
> +_ACEOF
> +if ac_fn_c_try_compile "$LINENO"; then :
> +  ac_cv_struct_tm=time.h
> +else
> +  ac_cv_struct_tm=sys/time.h
> +fi
> +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_struct_tm" >&5
> +$as_echo "$ac_cv_struct_tm" >&6; }
> +if test $ac_cv_struct_tm = sys/time.h; then
> +
> +$as_echo "#define TM_IN_SYS_TIME 1" >>confdefs.h
> +
> +fi
> +
> +ac_fn_c_check_member "$LINENO" "struct tm" "tm_zone"
> "ac_cv_member_struct_tm_tm_zone" "#include <sys/types.h>
> +#include <$ac_cv_struct_tm>
> +
> +"
> +if test "x$ac_cv_member_struct_tm_tm_zone" = xyes; then :
> +
> +cat >>confdefs.h <<_ACEOF
> +#define HAVE_STRUCT_TM_TM_ZONE 1
> +_ACEOF
> +
> +
> +fi
> +
> +if test "$ac_cv_member_struct_tm_tm_zone" = yes; then
> +
> +$as_echo "#define HAVE_TM_ZONE 1" >>confdefs.h
> +
> +else
> +  ac_fn_c_check_decl "$LINENO" "tzname" "ac_cv_have_decl_tzname"
> "#include <time.h>
> +"
> +if test "x$ac_cv_have_decl_tzname" = xyes; then :
> +  ac_have_decl=1
> +else
> +  ac_have_decl=0
> +fi
> +
> +cat >>confdefs.h <<_ACEOF
> +#define HAVE_DECL_TZNAME $ac_have_decl
> +_ACEOF
> +
> +  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for tzname" >&5
> +$as_echo_n "checking for tzname... " >&6; }
> +if ${ac_cv_var_tzname+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +  if test x$gcc_no_link = xyes; then
> +  as_fn_error $? "Link tests are not allowed after GCC_NO_EXECUTABLES."
> "$LINENO" 5
> +fi
> +cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +/* end confdefs.h.  */
> +#include <time.h>
> +#if !HAVE_DECL_TZNAME
> +extern char *tzname[];
> +#endif
> +
> +int
> +main ()
> +{
> +return tzname[0][0];
> +  ;
> +  return 0;
> +}
> +_ACEOF
> +if ac_fn_c_try_link "$LINENO"; then :
> +  ac_cv_var_tzname=yes
> +else
> +  ac_cv_var_tzname=no
> +fi
> +rm -f core conftest.err conftest.$ac_objext \
> +    conftest$ac_exeext conftest.$ac_ext
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_var_tzname" >&5
> +$as_echo "$ac_cv_var_tzname" >&6; }
> +  if test $ac_cv_var_tzname = yes; then
> +
> +$as_echo "#define HAVE_TZNAME 1" >>confdefs.h
> +
> +  fi
> +fi
> +
> +
>  # Define documentation rules conditionally.
>
>  # See if makeinfo has been installed and is modern enough
> diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
> index a3b257fe652..fe0cdde1f7a 100644
> --- a/libstdc++-v3/configure.ac
> +++ b/libstdc++-v3/configure.ac
> @@ -584,6 +584,8 @@ GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES
>  # For std::text_encoding
>  GLIBCXX_CHECK_TEXT_ENCODING
>
> +AC_STRUCT_TIMEZONE
> +
>  # Define documentation rules conditionally.
>
>  # See if makeinfo has been installed and is modern enough
> diff --git a/libstdc++-v3/include/bits/chrono_io.h
> b/libstdc++-v3/include/bits/chrono_io.h
> index 86338d48d18..08969166d2f 100644
> --- a/libstdc++-v3/include/bits/chrono_io.h
> +++ b/libstdc++-v3/include/bits/chrono_io.h
> @@ -894,13 +894,42 @@ namespace __format
>           // %Ec Locale's alternate date and time representation.
>
>           using namespace chrono;
> +         using ::std::chrono::__detail::__utc_leap_second;
> +         using ::std::chrono::__detail::__local_time_fmt;
> +
> +         struct tm __tm{};
> +
> +         // Some locales use %Z in their %c format but we don't want
> strftime
> +         // to use the system's local time zone (from /etc/localtime or
> $TZ)
> +         // as the output for %Z. Setting tm_isdst to -1 says there is no
> +         // time zone info available for the time in __tm.
> +         __tm.tm_isdst = -1;
> +
> +#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
> +         // POSIX.1-2024 adds tm.tm_zone which will be used for %Z.
> +         if constexpr (__is_time_point_v<_Tp>)
> +           {
> +             // One of sys_time, utc_time, or local_time.
> +             if constexpr (!is_same_v<typename _Tp::clock, local_t>)
> +               __tm.tm_zone = "UTC";
>
I have checked that other clocks, like TAI and GPS that user different zone
name,
are formatted using __local_time_fmt.

> +           }
> +         else if constexpr (__is_specialization_of<_Tp, __local_time_fmt>)
> +           {
> +             // local-time-format-t is used to provide time zone info for
> +             // one of zoned_time, tai_time, gps_time, or local_time.
> +             if (__t._M_abbrev)
> +               __tm.tm_zone = __t._M_abbrev->c_str();
> +           }
> +         else
> +           __tm.tm_zone = "UTC";
> +#endif
> +
>           auto __d = _S_days(__t); // Either sys_days or local_days.
>           using _TDays = decltype(__d);
>           const year_month_day __ymd(__d);
>           const auto __y = __ymd.year();
>           const auto __hms = _S_hms(__t);
>
> -         struct tm __tm{};
>           __tm.tm_year = (int)__y - 1900;
>           __tm.tm_yday = (__d - _TDays(__y/January/1)).count();
>           __tm.tm_mon = (unsigned)__ymd.month() - 1;
> @@ -909,6 +938,7 @@ namespace __format
>           __tm.tm_hour = __hms.hours().count();
>           __tm.tm_min = __hms.minutes().count();
>           __tm.tm_sec = __hms.seconds().count();
> +
>           return _M_locale_fmt(std::move(__out), _M_locale(__ctx), __tm,
> 'c',
>                                __mod ? 'E' : '\0');
>         }
> diff --git a/libstdc++-v3/testsuite/std/time/format/pr117214.cc
> b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
> index e7831832206..87c703dd255 100644
> --- a/libstdc++-v3/testsuite/std/time/format/pr117214.cc
> +++ b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
> @@ -28,7 +28,72 @@ test_c()
>    }
>  }
>
> +#include <stdlib.h>
> +#include <time.h>
> +
> +extern "C++" int tzset(int);
> +
> +template<typename T = void>
> +void maybe_set_tz()
> +{
> +#ifdef _GLIBCXX_HAVE_SETENV
> +  // True if a function 'T tzset()' has been declared.
> +  if constexpr (requires (T (*p)()) { p = &tzset; })
> +  {
> +    setenv("TZ", "GMT0", 1);
> +    tzset(); // Set C library's global time zone to GMT0
> +  }
> +#endif
> +}
> +
> +void
> +test_c_zoned()
> +{
> +#if _GLIBCXX_USE_CXX11_ABI
> +  maybe_set_tz();
> +
> +  using namespace std::chrono;
> +  auto time = sys_days(2025y/March/19) + 15h;
> +  zoned_time z("America/New_York", time);
> +  auto s = std::format(std::locale("aa_DJ.UTF-8"), "{:L%c}", z);
> +  VERIFY( s.find("11:00") != s.npos );
> +
> +  // We should not print an incorrect time zone.
> +  VERIFY( s.find("GMT") == s.npos );
> +  VERIFY( s.find("UTC") == s.npos );
> +
> +#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
> +  // When tm.tm_zone is supported, we do print the correct time zone.
> +  VERIFY( s.find(z.get_info().abbrev) != s.npos );
> +#endif
> +#endif
> +}
> +
> +void
> +test_c_local()
> +{
> +  maybe_set_tz();
> +
> +  std::locale("aa_DJ.UTF-8");
> +  using namespace std::chrono;
> +  auto time = local_days(2025y/March/19) + 11h;
> +  auto s = std::format(std::locale("aa_DJ.UTF-8"), "{:L%c}", time);
> +  // __builtin_printf("%s\n", s.c_str()); return;
> +  VERIFY( s.find("11:00") != s.npos );
> +
> +  // We should not print any time zone.
> +  VERIFY( s.find("GMT") == s.npos );
> +  VERIFY( s.find("UTC") == s.npos );
> +
> +#if _GLIBCXX_USE_CXX11_ABI
> +  zoned_time z(system_clock::now());
> +  VERIFY( s.find(z.get_info().abbrev) == s.npos );
> +#endif
> +}
> +
>  int main()
>  {
>    test_c();
> +  test_c_zoned();
> +  test_c_local();
>  }
> --
> 2.48.1
>
>

Re: [PATCH 3/3] libstdc++: Fix localized %c formatting for non-UTC times [PR117214]

[Jonathan Wakely]

On Fri, 21 Mar 2025 at 12:24, Tomasz Kaminski <tkaminsk@redhat.com> wrote:
>
>
>
> On Thu, Mar 20, 2025 at 10:39 AM Jonathan Wakely <jwakely@redhat.com> wrote:
>>
>> The previous commit fixed most cases of %c formatting, but it
>> incorrectly prints times using the system's local time zone. This only
>> matters if the locale's %c format includes %Z, but some do.
>>
>> To print a correct value for %Z we can set tm.tm_zone to either "UTC" or
>> the abbreviation passed to the formatter in the local-time-format-t
>> structure.
>>
>> For local times with no info and for systems that don't support tm_zone
>> (which is new in POSIX.1-2024) we just set tm_isdst = -1 so that no zone
>> name is printed.
>>
>> In theory, a locale's %c format could use %z which should print a +hhmm
>> offset from UTC. I'm unsure how to control that though. The new
>> tm_gmtoff field in combination with tm_isdst != -1 seems like it should
>> work, but using that without also setting tm_zone causes the system zone
>> to be used for %Z again. That means local_time_format(lt, nullptr, &off)
>> might work for a locale that uses %z but prints the wrong thing for %Z.
>> This commit doesn't set tm_gmtoff even if _M_offset_sec is provided for
>> a local-time-format-t value.
>>
>> libstdc++-v3/ChangeLog:
>>
>>         PR libstdc++/117214
>>         * configure.ac: Use AC_STRUCT_TIMEZONE.
>>         * config.h.in: Regenerate.
>>         * configure: Regenerate.
>>         * include/bits/chrono_io.h (__formatter_chrono::_M_c): Set
>>         tm_isdst and tm_zone.
>>         * testsuite/std/time/format/pr117214.cc: Check %c formatting of
>>         zoned_time and local time.
>> ---
>>
>> Tested x86_64-linux.
>
> The c++ code parts LGTM, however the changes in config.h.in and
> configure went over my head: they seem to check for new members,
> but I cannot confirm if they are correct and according to best practices.

It's all generated by autoconf. The only change is adding
AC_STRUCT_TIMEZONE to configure.ac which is documented at
https://www.gnu.org/software/autoconf/manual/autoconf-2.64/html_node/Particular-Structures.html#Particular-Structures
The rest is just what autoconf generates from that, and so doesn't
need to be reviewed.


>> diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
>> index a3b257fe652..fe0cdde1f7a 100644
>> --- a/libstdc++-v3/configure.ac
>> +++ b/libstdc++-v3/configure.ac
>> @@ -584,6 +584,8 @@ GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES
>>  # For std::text_encoding
>>  GLIBCXX_CHECK_TEXT_ENCODING
>>
>> +AC_STRUCT_TIMEZONE
>> +
>>  # Define documentation rules conditionally.
>>
>>  # See if makeinfo has been installed and is modern enough
>> diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
>> index 86338d48d18..08969166d2f 100644
>> --- a/libstdc++-v3/include/bits/chrono_io.h
>> +++ b/libstdc++-v3/include/bits/chrono_io.h
>> @@ -894,13 +894,42 @@ namespace __format
>>           // %Ec Locale's alternate date and time representation.
>>
>>           using namespace chrono;
>> +         using ::std::chrono::__detail::__utc_leap_second;
>> +         using ::std::chrono::__detail::__local_time_fmt;
>> +
>> +         struct tm __tm{};
>> +
>> +         // Some locales use %Z in their %c format but we don't want strftime
>> +         // to use the system's local time zone (from /etc/localtime or $TZ)
>> +         // as the output for %Z. Setting tm_isdst to -1 says there is no
>> +         // time zone info available for the time in __tm.
>> +         __tm.tm_isdst = -1;
>> +
>> +#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
>> +         // POSIX.1-2024 adds tm.tm_zone which will be used for %Z.
>> +         if constexpr (__is_time_point_v<_Tp>)
>> +           {
>> +             // One of sys_time, utc_time, or local_time.
>> +             if constexpr (!is_same_v<typename _Tp::clock, local_t>)
>> +               __tm.tm_zone = "UTC";
>
> I have checked that other clocks, like TAI and GPS that user different zone name,
> are formatted using __local_time_fmt.

Thanks!

>>
>> +           }
>> +         else if constexpr (__is_specialization_of<_Tp, __local_time_fmt>)
>> +           {
>> +             // local-time-format-t is used to provide time zone info for
>> +             // one of zoned_time, tai_time, gps_time, or local_time.
>> +             if (__t._M_abbrev)
>> +               __tm.tm_zone = __t._M_abbrev->c_str();
>> +           }
>> +         else
>> +           __tm.tm_zone = "UTC";
>> +#endif
>> +
>>           auto __d = _S_days(__t); // Either sys_days or local_days.
>>           using _TDays = decltype(__d);
>>           const year_month_day __ymd(__d);
>>           const auto __y = __ymd.year();
>>           const auto __hms = _S_hms(__t);
>>
>> -         struct tm __tm{};
>>           __tm.tm_year = (int)__y - 1900;
>>           __tm.tm_yday = (__d - _TDays(__y/January/1)).count();
>>           __tm.tm_mon = (unsigned)__ymd.month() - 1;
>> @@ -909,6 +938,7 @@ namespace __format
>>           __tm.tm_hour = __hms.hours().count();
>>           __tm.tm_min = __hms.minutes().count();
>>           __tm.tm_sec = __hms.seconds().count();
>> +
>>           return _M_locale_fmt(std::move(__out), _M_locale(__ctx), __tm, 'c',
>>                                __mod ? 'E' : '\0');
>>         }
>> diff --git a/libstdc++-v3/testsuite/std/time/format/pr117214.cc b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
>> index e7831832206..87c703dd255 100644
>> --- a/libstdc++-v3/testsuite/std/time/format/pr117214.cc
>> +++ b/libstdc++-v3/testsuite/std/time/format/pr117214.cc
>> @@ -28,7 +28,72 @@ test_c()
>>    }
>>  }
>>
>> +#include <stdlib.h>
>> +#include <time.h>
>> +
>> +extern "C++" int tzset(int);
>> +
>> +template<typename T = void>
>> +void maybe_set_tz()
>> +{
>> +#ifdef _GLIBCXX_HAVE_SETENV
>> +  // True if a function 'T tzset()' has been declared.
>> +  if constexpr (requires (T (*p)()) { p = &tzset; })
>> +  {
>> +    setenv("TZ", "GMT0", 1);
>> +    tzset(); // Set C library's global time zone to GMT0
>> +  }
>> +#endif
>> +}
>> +
>> +void
>> +test_c_zoned()
>> +{
>> +#if _GLIBCXX_USE_CXX11_ABI
>> +  maybe_set_tz();
>> +
>> +  using namespace std::chrono;
>> +  auto time = sys_days(2025y/March/19) + 15h;
>> +  zoned_time z("America/New_York", time);
>> +  auto s = std::format(std::locale("aa_DJ.UTF-8"), "{:L%c}", z);
>> +  VERIFY( s.find("11:00") != s.npos );
>> +
>> +  // We should not print an incorrect time zone.
>> +  VERIFY( s.find("GMT") == s.npos );
>> +  VERIFY( s.find("UTC") == s.npos );
>> +
>> +#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
>> +  // When tm.tm_zone is supported, we do print the correct time zone.
>> +  VERIFY( s.find(z.get_info().abbrev) != s.npos );
>> +#endif
>> +#endif
>> +}
>> +
>> +void
>> +test_c_local()
>> +{
>> +  maybe_set_tz();
>> +
>> +  std::locale("aa_DJ.UTF-8");
>> +  using namespace std::chrono;
>> +  auto time = local_days(2025y/March/19) + 11h;
>> +  auto s = std::format(std::locale("aa_DJ.UTF-8"), "{:L%c}", time);
>> +  // __builtin_printf("%s\n", s.c_str()); return;
>> +  VERIFY( s.find("11:00") != s.npos );
>> +
>> +  // We should not print any time zone.
>> +  VERIFY( s.find("GMT") == s.npos );
>> +  VERIFY( s.find("UTC") == s.npos );
>> +
>> +#if _GLIBCXX_USE_CXX11_ABI
>> +  zoned_time z(system_clock::now());
>> +  VERIFY( s.find(z.get_info().abbrev) == s.npos );
>> +#endif
>> +}
>> +
>>  int main()
>>  {
>>    test_c();
>> +  test_c_zoned();
>> +  test_c_local();
>>  }
>> --
>> 2.48.1
>>