Add utc methods for trantor::Date. (#218)

Author: hwc0919

trantor/utils/Date.cc

@@ -274,6 +274,11 @@ std::string Date::toDbStringLocal() const
     }
     return buf;
 }
+std::string Date::toDbString() const
+{
+    return after(static_cast<double>(-timezoneOffset())).toDbStringLocal();
+}
+
 Date Date::fromDbStringLocal(const std::string &datetime)
 {
     unsigned int year = {0}, month = {0}, day = {0}, hour = {0}, minute = {0},
@@ -312,6 +317,12 @@ Date Date::fromDbStringLocal(const std::string &datetime)
     }
     return trantor::Date(year, month, day, hour, minute, second, microSecond);
 }
+Date Date::fromDbString(const std::string &datetime)
+{
+    return fromDbStringLocal(datetime).after(
+        static_cast<double>(timezoneOffset()));
+}
+
 std::string Date::toCustomedFormattedStringLocal(const std::string &fmtStr,
                                                  bool showMicroseconds) const
 {

trantor/utils/Date.h

@@ -74,6 +74,13 @@ class TRANTOR_EXPORT Date
         return Date::date();
     }
 
+    static int64_t timezoneOffset()
+    {
+        static int64_t offset =
+            0 - Date::fromDbStringLocal("1970-01-01").secondsSinceEpoch();
+        return offset;
+    }
+
     /**
      * @brief Return a new Date instance that represents the time after some
      * seconds from *this.
@@ -233,13 +240,23 @@ class TRANTOR_EXPORT Date
      * is zero 2018-01-01 10:10:25:102414   //If the microsecond is not zero
      */
     std::string toDbStringLocal() const;
+    /**
+     * @brief Generate a UTC time string for database.
+     */
+    std::string toDbString() const;
 
     /**
      * @brief From DB string to trantor local time zone.
      *
      * Inverse of toDbStringLocal()
      */
     static Date fromDbStringLocal(const std::string &datetime);
+    /**
+     * @brief From DB string to trantor UTC time.
+     *
+     * Inverse of toDbString()
+     */
+    static Date fromDbString(const std::string &datetime);
 
     /**
      * @brief Generate a UTC time string.