fix UB in on_second

fmtlib · Jun 3, 2019 · 3716491 · 3716491
1 parent 2740241
commit 3716491
Showing 1 changed file with 13 additions and 1 deletion.
diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
@@ -660,7 +660,19 @@ struct chrono_formatter {
 
     if (ns == numeric_system::standard) {
       write(second(), 2);
-      auto ms = get_milliseconds(std::chrono::duration<Rep, Period>(val));
+#ifdef FMT_SAFE_DURATION_CAST
+    int ec;
+    //convert rep->Rep
+    using Crep=std::chrono::duration<rep, Period>;
+    using CRep=std::chrono::duration<Rep, Period>;
+    auto tmpval = safe_duration_cast::safe_duration_cast<CRep>(Crep{val}, ec);
+    if (ec) {
+      FMT_THROW(format_error("value would cause UB or the wrong result"));
+    }
+#else
+      auto tmpval=std::chrono::duration<Rep, Period>(val);
+#endif
+      auto ms = get_milliseconds(tmpval);
       if (ms != std::chrono::milliseconds(0)) {
         *out++ = '.';
         write(ms.count(), 3);