tzdb.cpp: Fall back to numeric offset when the current code page cannot represent the time zone short ID (#5558)

cpplearner · StephanTLavavej · web-flow · commit 029ce565100d · 2025-06-14T03:06:35.000-07:00
Co-authored-by: Stephan T. Lavavej &lt;stl@microsoft.com&gt;
diff --git a/stl/src/tzdb.cpp b/stl/src/tzdb.cpp
@@ -567,7 +567,31 @@ void __stdcall __std_tzdb_delete_current_zone(__std_tzdb_current_zone_info* cons
 
     _Info->_Abbrev = _Allocate_wide_to_narrow(_Abbrev.get(), _Abbrev_len, _Info->_Err);
     if (_Info->_Abbrev == nullptr) {
-        return _Propagate_error(_Info);
+        const auto _Abs_offset        = _Info->_Offset < 0 ? -_Info->_Offset : _Info->_Offset;
+        const auto _Offset_in_minutes = _Abs_offset / (60 * 1000);
+        const auto _Hours             = _Offset_in_minutes / 60;
+        const auto _Mins              = _Offset_in_minutes % 60;
+
+        _STD unique_ptr<char[]> _Fallback_abbrev{new (_STD nothrow) char[_Mins == 0 ? 4 : 6]};
+
+        if (_Fallback_abbrev == nullptr) {
+            return nullptr;
+        }
+
+        _Fallback_abbrev[0] = _Info->_Offset < 0 ? '-' : '+';
+        _Fallback_abbrev[1] = static_cast<char>('0' + _Hours / 10);
+        _Fallback_abbrev[2] = static_cast<char>('0' + _Hours % 10);
+
+        if (_Mins == 0) {
+            _Fallback_abbrev[3] = '\0';
+        } else {
+            _Fallback_abbrev[3] = static_cast<char>('0' + _Mins / 10);
+            _Fallback_abbrev[4] = static_cast<char>('0' + _Mins % 10);
+            _Fallback_abbrev[5] = '\0';
+        }
+
+        _Info->_Err    = __std_tzdb_error::_Success;
+        _Info->_Abbrev = _Fallback_abbrev.release();
     }
 
     return _Info.release();
