Overview

• This value type represents dates and times.
  • Its values ranges from 00:00:00 (midnight), January 1, 0001 Anno Domini through 11:59:59 P.M., December 31, 9999 A.D. in the Gregorian calendar.
  • Internally, all DateTime values are represented as the number of ticks (the number of 100-nanosecond intervals) that have elapsed since 12:00:00 midnight, January 1, 0001.
  • The actual DateTime value is independent of the way in which that value appears when displayed in a user interface element or when written to a file.
  • The appearance of a DateTime value is the result of a formatting operation.
    • For example, a ticks value of 31241376000000000L represents the date, Friday, January 01, 0100 12:00:00 midnight.
• The DateTime structure contains a 64-bit field composed of a private Kind field concatenated with the Ticks field.
  • The Kind field is a 2-bit field that indicates whether the DateTime structure represents a local time, a Coordinated Universal Time (UTC), or the time in an unspecified time zone.
  • The Kind field is used when performing time conversions between time zones, but not for time comparisons or arithmetic. The value of the Kind field can be obtained with the Kind property.
• The Ticks property expresses date and time values in units of one ten-millionth of a second, and the Millisecond property returns the thousandths of a second in a date and time value.
  • However, if you are using repeated calls to the DateTime.Now property to measure elapsed time, and you are concerned with small time intervals less than 100 milliseconds, you should note that values returned by the DateTime.Now property are dependent on the system clock, which on Windows 7 and Windows 8 systems has a resolution of approximately 15 milliseconds.
• A DateTime value is always expressed in the context of an explicit or default calendar.
• If you are working with a ticks value that you want to convert to some other time interval, such as minutes or seconds, you should use the TimeSpan.TicksPerDay, TimeSpan.TicksPerHour, TimeSpan.TicksPerMinute, TimeSpan.TicksPerSecond, or TimeSpan.TicksPerMillisecond constant to perform the conversion.
• ParseExact and TryParseExact allow you to specify the format of the date in the containing input string before you parse the value.
• ParseExact() is also useful if you want to only accept one format as valid (even if it’s a standard format).
• If you know the exact format that the date time representation should be, ParseExact() is more efficient than Parse().
• Note that custom format strings are case sensitive.
  • For example, “MM” is months and “mm” is minutes, “HH” is 24-hour format and “hh” is 12-hour format, “mm” is zero-padded where “m” is not, etc.
• Also notice that in the snippet below we passed a null for the IFormatProvider.
  • Doing this uses the current culture’s DateTime format provider.

logEntryTime = DateTime.ParseExact(logString, "yyyyMMdd HHmmss", null);
logEntryTime = DateTime.ParseExact(logString, "yyyyMMdd hhmmss", DateTimeFormatInfo.CurrentInfo);

Custom Date and Time Format Strings

How to: convert strings to DateTime

• Note that the TryParse and TryParseExact methods indicate whether a particular string contains a valid representation of a DateTime value in addition to performing the conversion.
• A calculation using a DateTime structure, such as Add or Subtract, does not modify the value of the structure.
  • Instead, the calculation returns a new DateTime structure whose value is the result of the calculation.
• Conversion operations between time zones (such as between UTC and local time, or between one time zone and another) take daylight saving time into account, but arithmetic and comparison operations do not.
• The DateTime structure itself offers limited support for converting from one time zone to another.
  • You can use the ToLocalTime method to convert UTC to local time, or you can use the ToUniversalTime method to convert from local time to UTC.
  • However, a full set of time zone conversion methods is available in the TimeZoneInfo class.
  • Using these methods, you can convert the time in any time zones to the time in any other time zone.
• The default DateTime.ToString() method returns the string representation value using the current culture's short date and long time pattern.
• Parsing involves converting the string representation of a date and time to a DateTime value.
• You can use the TryParse and TryParseExact methods to convert a date and time string that must match a particular format or formats to a DateTime value. You specify the required format or formats as a parameter to the parsing methodby using one or more or date and time format strings.