TimeZoneInfo.GetAdjustmentRules Method

Definition

Retrieves an array of TimeZoneInfo.AdjustmentRule objects that apply to the current TimeZoneInfo object.

C#
public TimeZoneInfo.AdjustmentRule[] GetAdjustmentRules();

Returns

An array of objects for this time zone.

Exceptions

The system does not have enough memory to make an in-memory copy of the adjustment rules.

Examples

The following example retrieves all time zones that are defined on the local system and displays complete information about their adjustment rules to the console.

C#
private enum WeekOfMonth 
{
   First = 1,
   Second = 2,
   Third = 3,
   Fourth = 4,
   Last = 5,
}

private static void ShowStartAndEndDates()
{
   // Get all time zones from system
   ReadOnlyCollection<TimeZoneInfo> timeZones = TimeZoneInfo.GetSystemTimeZones();
   string[] monthNames = CultureInfo.CurrentCulture.DateTimeFormat.MonthNames;
   // Get each time zone
   foreach (TimeZoneInfo timeZone in timeZones)
   {
      TimeZoneInfo.AdjustmentRule[] adjustments = timeZone.GetAdjustmentRules();
      // Display message for time zones with no adjustments
      if (adjustments.Length == 0)
      {
         Console.WriteLine("{0} has no adjustment rules", timeZone.StandardName);
      }   
      else
      {
         // Handle time zones with 1 or 2+ adjustments differently
         bool showCount = false;
         int ctr = 0;
         string spacer = "";
         
         Console.WriteLine("{0} Adjustment rules", timeZone.StandardName);
         if (adjustments.Length > 1)
         {
            showCount = true;
            spacer = "   ";
         }   
         // Iterate adjustment rules
         foreach (TimeZoneInfo.AdjustmentRule adjustment in adjustments)
         {
            if (showCount)
            { 
               Console.WriteLine("   Adjustment rule #{0}", ctr+1);
               ctr++;
            }
            // Display general adjustment information
            Console.WriteLine("{0}   Start Date: {1:D}", spacer, adjustment.DateStart);
            Console.WriteLine("{0}   End Date: {1:D}", spacer, adjustment.DateEnd);
            Console.WriteLine("{0}   Time Change: {1}:{2:00} hours", spacer, 
                              adjustment.DaylightDelta.Hours, adjustment.DaylightDelta.Minutes);
            // Get transition start information
            TimeZoneInfo.TransitionTime transitionStart = adjustment.DaylightTransitionStart;
            Console.Write("{0}   Annual Start: ", spacer);
            if (transitionStart.IsFixedDateRule)
            {
               Console.WriteLine("On {0} {1} at {2:t}", 
                                 monthNames[transitionStart.Month - 1], 
                                 transitionStart.Day, 
                                 transitionStart.TimeOfDay);
            }
            else
            {
               Console.WriteLine("The {0} {1} of {2} at {3:t}", 
                                 ((WeekOfMonth)transitionStart.Week).ToString(), 
                                 transitionStart.DayOfWeek.ToString(), 
                                 monthNames[transitionStart.Month - 1], 
                                 transitionStart.TimeOfDay);
            }
            // Get transition end information
            TimeZoneInfo.TransitionTime transitionEnd = adjustment.DaylightTransitionEnd;
            Console.Write("{0}   Annual End: ", spacer);
            if (transitionEnd.IsFixedDateRule)
            {
               Console.WriteLine("On {0} {1} at {2:t}", 
                                 monthNames[transitionEnd.Month - 1], 
                                 transitionEnd.Day, 
                                 transitionEnd.TimeOfDay);
            }
            else
            {
               Console.WriteLine("The {0} {1} of {2} at {3:t}", 
                                 ((WeekOfMonth)transitionEnd.Week).ToString(), 
                                 transitionEnd.DayOfWeek.ToString(), 
                                 monthNames[transitionEnd.Month - 1], 
                                 transitionEnd.TimeOfDay);
            }
         }
      }   
      Console.WriteLine();
   } 
}

Remarks

The GetAdjustmentRules method retrieves an array of System.TimeZoneInfo.AdjustmentRule objects. Each object in the array defines the effective start and end date of that time zone adjustment, as well as its delta (the exact amount by which the adjustment causes the time to change). In addition, two properties return System.TimeZoneInfo.TransitionTime objects that define when each annual transition to and from standard time occurs.

If a time zone has multiple adjustment rules, they are generally ordered from earliest (at index 0) to latest (at index Length - 1).

If a time zone has no adjustment rules, the GetAdjustmentRules method returns an empty array (an array whose Length is zero).

Any modifications to the elements of the array returned by the GetAdjustmentRules method are not reflected in the adjustment rules that belong to a particular time zone. To modify a time zone's adjustment rules (such as to reflect its historical transition to and from daylight saving time) you must create a new time zone with the appropriate adjustment rules, rather than modify the existing one.

Applies to

Product Versions
.NET Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 2.0, 2.1

See also