Thai year 2558 to 2015

Question

How to transform buddhist format of datetime into gregorian format (e.g. for Thailand 2558 → 2015)?

using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ThailandBuddhistCalendarTest
{
    class Program
    {
        private const string DateFormat = "yyyy-MM-dd";
        private const string DateTimeOffsetFormat = "yyyy-MM-dd'T'HH:mm:sszzz";

        static void Main(string[] args)
        {
            var ci = new CultureInfo("th-TH");
            var today = DateTime.Now.ToString(DateFormat, ci); // today == "2558-05-22"
        }
    }
}

Answer 1

The simple answer to your question is, use a Culture which is using the GregorianCalendar as format provider, just like Soner Gönül suggest at the end of his answer.

However, do not try to adjust the DateTime so that its Year property would show 2558 instead of 2015.

Even when the DateTime does not use a specific calendar for the stored date, it's properties always give the date and time parts based on the gregorian calendar. This leads to following:

buddhistCalendar.ToDateTime(2558,5,22,0,0,0,0) != new DateTime(2558,5,22,0,0,0,0)

but:

buddhistCalendar.ToDateTime(2558,5,22,0,0,0,0) == new DateTime(2015,5,22,0,0,0,0)

If you want to get the year, or any other value, of a given DateTime for a specific calendar, then use the appropriate method form that calendar like calendar.GetYear(dateTime).

Otherwise you would get

new DateTime(2558,5,22,0,0,0,0).Year == 2558

but:

buddhistCalendar.GetYear(new DateTime(2558,5,22,0,0,0,0)) == 3101

Answer 2

Take a look at the ThaiBuddhistCalendar class.

In example, if you know thai year, you can do this:

ThaiBuddhistCalendar cal = new ThaiBuddhistCalendar();
cal.ToDateTime(2558, 2, 1, 0, 0, 0, 0);
.ToString("yyyy-MM-dd") // returns 2015-01-01

If you need get Thai DateTime, you can do this:

ThaiBuddhistCalendar cal = new ThaiBuddhistCalendar();
DateTime now = DateTime.Now;
DateTime thai = new DateTime(cal.GetYear(now), cal.GetMonth(now), now.Day);

Answer 3

DateTime.Now generates your local time with GregorianCalender by default. If you wanna generate that time in your ThaiBuddhistCalendar, you can get it's values with an instance of that calender object.

Now you can use this values in DateTime(Int32, Int32, Int32, Int32, Int32, Int32) constructor to generate a DateTime.

After that, you can format your DateTime with a specific format.

var now = DateTime.Now;
int thaiYear = new ThaiBuddhistCalendar().GetYear(now);
int thaiMonth = new ThaiBuddhistCalendar().GetMonth(now);
int thaiDay = new ThaiBuddhistCalendar().GetDayOfMonth(now);
int thaiHour = new ThaiBuddhistCalendar().GetHour(now);
int thaiMinute = new ThaiBuddhistCalendar().GetMinute(now);
int thaiSecond = new ThaiBuddhistCalendar().GetSecond(now);

var thaiDateTime = new DateTime(thaiYear, thaiMonth, thaiDay, thaiHour, thaiMinute, thaiSecond);
Console.WriteLine(thaiDateTime.ToString("yyyy-MM-dd"));

Result will be;

2558-05-22

From http://www.thaiworldview.com/feast/feast.htm

There is a 543 years difference between the Buddhist calendar and the Gregorian calendar. Year 2015 in Europe is year 2558 in Thailand.

If you looking for the opposite way, just use a culture that have Gregorian calender as a Calender part like InvariantCulture.

var today = DateTime.Now.ToString(DateFormat, CultureInfo.InvariantCulture)); // 2015-05-22