Add platform-specific 'z' formatter

fmtlib · Nov 14, 2021 · 76da43b · 76da43b
1 parent 8dc1153
commit 76da43b
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Showing 3 changed files with 49 additions and 1 deletion.
diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
@@ -988,6 +988,18 @@ template <typename OutputIt, typename Char> class tm_writer {
     }
   }
 
+  void write_utc_offset(long offset) {
+    if (offset < 0) {
+      *out_++ = '-';
+      offset = -offset;
+    } else {
+      *out_++ = '+';
+    }
+    offset /= 60;
+    write2(static_cast<int>(offset / 60));
+    write2(static_cast<int>(offset % 60));
+  }
+
   void format_localized(char format, char modifier = 0) {
     out_ = write<Char>(out_, tm_, loc_, format, modifier);
   }
@@ -1093,7 +1105,29 @@ template <typename OutputIt, typename Char> class tm_writer {
     out_ = copy_str<Char>(std::begin(buf) + offset, std::end(buf), out_);
   }
 
-  void on_utc_offset() { format_localized('z'); }
+  void on_utc_offset() {
+#if defined(_WIN32)
+    _tzset();
+    long offset = 0;
+    _get_timezone(&offset);
+    if (tm_.tm_isdst) {
+      long dstbias = 0;
+      _get_dstbias(&dstbias);
+      offset += dstbias;
+    }
+    write_utc_offset(-offset);
+#elif defined(__APPLE__) || defined(__GLIBC__) || defined(__FreeBSD__) || \
+    defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
+    write_utc_offset(tm_.tm_gmtoff);
+#elif defined(sun) || defined(__sun)
+    tzset();
+    write_utc_offset(
+        static_cast<long>(tm_.tm_isdst == 0 ? -timezone : -altzone));
+#else
+    // For exotic platforms.
+    format_localized('z');
+#endif
+  }
   void on_tz_name() { format_localized('Z'); }
 
   void on_year(numeric_system ns) {

diff --git a/test/chrono-test.cc b/test/chrono-test.cc
@@ -49,7 +49,14 @@ std::string system_strftime(const std::string& format, const std::tm* timeptr,
   os.imbue(loc);
   facet.put(os, os, ' ', timeptr, format.c_str(),
             format.c_str() + format.size());
+#ifdef _WIN32
+  // Workaround to early ucrt bug
+  auto str = os.str();
+  if (str == "-0000") str = "+0000";
+  return str;
+#else
   return os.str();
+#endif
 }
 
 FMT_CONSTEXPR std::tm make_tm(int year, int mon, int mday, int hour, int min,

diff --git a/test/xchar-test.cc b/test/xchar-test.cc
@@ -277,7 +277,14 @@ std::wstring system_wcsftime(const std::wstring& format, const std::tm* timeptr,
   os.imbue(loc);
   facet.put(os, os, L' ', timeptr, format.c_str(),
             format.c_str() + format.size());
+#ifdef _WIN32
+  // Workaround to early ucrt bug
+  auto str = os.str();
+  if (str == L"-0000") str = L"+0000";
+  return str;
+#else
   return os.str();
+#endif
 }
 
 TEST(chrono_test, time_point) {