DateTime String Format Extensions

Bear in mind that a DateTime should generally be stored in Universal format and converted to local format when be displayed in a GUI or used in a report. This handy extension for date time format strings saves having to remember their obscure format codes or look them up every time.

// See here for more info 
// https://docs.microsoft.com/en-us/dotnet/standard/base-types/standard-date-and-time-format-strings
public static class DateTimeToStringExtender
{
    public static bool ParseGeneralShortDateTime(this string dateTimeStr, out DateTime dateTime)
    {
        var format = "g"; // Standard short date time format: "dd/MM/yyyy HH:mm:ss" for UK
        bool result = false;
        CultureInfo provider = CultureInfo.CurrentCulture;
        result = DateTime.TryParseExact(dateTimeStr.Trim(), format, provider, DateTimeStyles.None, out dateTime);
        return result;
    }

    /// <summary>
    /// Convert a DateTime to a YearMonthDay string of the form yyyy/MM/dd
    /// </summary>
    /// <param name="dt">target</param>
    /// <returns>YearMonthDay string of the form yyyyMMdd</returns>
    public static string ToYyyyMmDdString(this DateTime dt, char separator = char.MinValue)
    {
        string format = "yyyyMMdd";
        if (!char.IsControl(separator))
        {
            format = "yyyy" + separator + "MM" + separator + "dd";
        }
        var res = dt.ToString(format);
        return res;
    }

    /// <summary>
    /// Convert a DateTime to a YearMonthDay string of the form DdMmYyyy
    /// </summary>
    /// <param name="dt">target</param>
    /// <returns>YearMonthDay string of the form DdMmYyyy</returns>
    public static string ToDdMmYyyyString(this DateTime dt, char separator = char.MinValue)
    {
        string format = "ddMMyyyy";
        if (!char.IsControl(separator))
        {
            format = "dd" + separator + "MM" + separator + "yyyy";
        }
        return dt.ToString(format);
    }


    /// <summary>
    /// Convert a DateTime to a YearMonthDay string of the form yyyyMMdd_HHmmss where the hour is in the 24 hour format
    /// </summary>
    /// <param name="dt">target</param>
    /// <returns>YearMonthDay string of the form yyyyMMdd_HHmmss</returns>
    public static string ToYyyyMmDd_HhMmSsString(this DateTime dt)
    {
        return dt.ToString("yyyyMMdd_HHmmss");
    }

    /// <summary>
    /// Convert a DateTime to a YearMonthDay string of the form yyyyMMdd_HHmmss_ffffff where the hour is in the 24 hour format
    /// Useful for creating randomised filenames based upon the date
    /// </summary>
    /// <param name="dt">target</param>
    /// <returns>YearMonthDay string of the form yyyyMMdd_HHmmss_ffffff</returns>
    public static string To_YyyyMmDd_HhMmSs_ffffff(this DateTime dt)
    {
        return dt.ToString("yyyyMMdd_HHmmss_ffffff");
    }

    /// <summary>
    /// Convert a DateTime to a YearMonthDay string of the form yyyyMMdd_HHmmss where the hour is in the 24 hour format
    /// </summary>
    /// <param name="dt">target</param>
    /// <returns>YearMonthDay string of the form yyyyMMdd_HHmmss</returns>
    public static string ToYyyyMmDd_HhMmSsString(this DateTime dt, char dateSeparator = char.MinValue, char timeSeparator = char.MinValue)
    {
        string format = "yyyyMMdd_HHmmss";
        if (!char.IsLetterOrDigit(dateSeparator) && !char.IsControl(dateSeparator))
        {
            format = "yyyy" + dateSeparator + "MM" + dateSeparator + "dd" + "_" + "HH" + timeSeparator + "mm" + timeSeparator + "ss";
        }
        return dt.ToString(format);
    }


    /// <summary>
    /// Emits a date time (culture independent) string of the form 
    /// "ddd, dd MMM yyyy HH':'mm':'ss 'GMT'"
    /// (eg.: "Sun, 09 Mar 2008 16:05:07 GMT"). 
    /// Works on universal date times only
    /// </summary>
    /// <param name="dateTime">target date time to convert to a string</param>
    /// <returns>dateTime formatted as a string</returns>
    public static string ToRfc1123FormatString(this DateTime dateTime)
    {
        string result = dateTime.ToUniversalTime().ToString("r");
        return result;
    }

    /// <summary>
    /// Convert a DateTime to a string of the form "2008-03-09 16:05:07Z"
    /// where the '-' character is culture dependant
    /// </summary>
    /// <param name="dt">target</param>
    /// <returns>string of the form "2008-03-09 16:05:07Z" where '-' character is culture dependant</returns>
    public static string ToUniversalSorta­bleString(this DateTime dt)
    {
        return dt.ToUniversalTime().ToString("u");
    }

    // 2009-06-15T13:45:30 --> Monday, June 15, 2009 8:45:30 PM (for en-US)
    public static string ToUniversalFull(this DateTime dateTime)
    {
        var res = dateTime.ToUniversalTime().ToString("U");
        return res;
    }

    /// <summary>
    /// Emits a sortable date time (culture independent) string of the form "yyyy'-'MM'-'dd'T'HH':'mm':'ss" (eg.: "2008-03-09T16:05:07"")
    /// </summary>
    /// <param name="dateTime">target date time to convert to a string</param>
    /// <returns>dateTime formatted as a string</returns>
    public static string ToSortableFormatString(this DateTime dateTime)
    {
        string result = dateTime.ToString("s");
        return result;
    }

    /// <summary>
    /// Emits a result date time format string using a pattern that preserves
    /// time zone information and emits a result string that complies with
    /// ISO 8601 ("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffffffK"), preserves 
    /// the DateTime kind.
    /// </summary>
    /// <param name="dateTime">target date time to convert to a string</param>
    /// <returns>dateTime formatted as a string</returns>
    // 2009-06-15T13:45:30 (DateTimeKind.Utc) -->; 2009-06-15T13:45:30.0000000Z
    // 2009-06-15T13:45:30 (DateTimeKind.Local) --> 2009-06-15T13:45:30.0000000-07:00 (depending on the time zone)
    // 2009-06-15T13:45:30 (DateTimeKind.Unspecified) --> 2009-06-15T13:45:30.0000000
    public static string ToRoundTripFormatString(this DateTime dateTime)
    {
        string result = dateTime.ToString("o");
        return result;
    }

    static readonly string[] formats = { 
    // Extended formats
    "o",
    "yyyy-MM-ddTHH:mm:ss.ffffffZ",
    "yyyy-MM-ddTHH:mm:ss.fffffZ",
    "yyyy-MM-ddTHH:mm:ss.ffffZ",
    "yyyy-MM-ddTHH:mm:ss.fffZ",
    "yyyy-MM-ddTHH:mm:ss.ffZ",
    "yyyy-MM-ddTHH:mm:ss.fZ",
    "yyyy-MM-ddTHH:mm:ssZ"
  };

    public static DateTime ParseToIso8601DateTime(this string str)
    {
        return DateTime.ParseExact(str, formats,
            CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind);
    }

}