https://gcc.gnu.org/g:778c28c70f8573f8256c810ff0d9e143ff75dec3
commit r15-8491-g778c28c70f8573f8256c810ff0d9e143ff75dec3
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Mar 19 22:05:28 2025 +0000
libstdc++: Fix localized %c formatting for non-UTC times [PR117214]
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.
Diff:
---
libstdc++-v3/config.h.in | 18 +++
libstdc++-v3/configure | 179 ++++++++++++++++++++-
libstdc++-v3/configure.ac | 2 +
libstdc++-v3/include/bits/chrono_io.h | 32 +++-
libstdc++-v3/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 91e920044ee4..be151f43dd68 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 78758285f211..67d2b8c7b72c 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 a3b257fe6528..fe0cdde1f7ac 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 86338d48d183..08969166d2f7 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 e78318322065..87c703dd2554 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();
}
