there is an unknown word starting at index

C#: Parsing DateTime with TimeZone

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I was writing code to parse the RSS Feed XML files the other day and I was getting exceptions on the published date.  The was happening because of the special format which is not supported by .NET. The published dates had the format:

Mon, 02 February 2009, 16:52:10 AEST

The names of the time zones are not supported by .NET because they are not unique. Different time zones in the world can have the same abbreviation.

If you try to parse this string using Convert.ToDateTime method the following error is shown:

System.FormatException: The string was not recognized as a valid DateTime. There is an unknown word starting at index XYZ.

 

To handle this situation I have written this piece of code as a separate class called Utils. The array is a private member of the class.

private static string[][] TimeZones = new string[][] {
    new string[] {"ACDT", "+1030", "Australian Central Daylight"},
    new string[] {"ACST", "+0930", "Australian Central Standard"},
    new string[] {"ADT", "-0300", "(US) Atlantic Daylight"},
    new string[] {"AEDT", "+1100", "Australian East Daylight"},
    new string[] {"AEST", "+1000", "Australian East Standard"},
    new string[] {"AHDT", "-0900", ""},
    new string[] {"AHST", "-1000", ""},
    new string[] {"AST", "-0400", "(US) Atlantic Standard"},
    new string[] {"AT", "-0200", "Azores"},
    new string[] {"AWDT", "+0900", "Australian West Daylight"},
    new string[] {"AWST", "+0800", "Australian West Standard"},
    new string[] {"BAT", "+0300", "Bhagdad"},
    new string[] {"BDST", "+0200", "British Double Summer"},
    new string[] {"BET", "-1100", "Bering Standard"},
    new string[] {"BST", "-0300", "Brazil Standard"},
    new string[] {"BT", "+0300", "Baghdad"},
    new string[] {"BZT2", "-0300", "Brazil Zone 2"},
    new string[] {"CADT", "+1030", "Central Australian Daylight"},
    new string[] {"CAST", "+0930", "Central Australian Standard"},
    new string[] {"CAT", "-1000", "Central Alaska"},
    new string[] {"CCT", "+0800", "China Coast"},
    new string[] {"CDT", "-0500", "(US) Central Daylight"},
    new string[] {"CED", "+0200", "Central European Daylight"},
    new string[] {"CET", "+0100", "Central European"},
    new string[] {"CST", "-0600", "(US) Central Standard"},
    new string[] {"CENTRAL", "-0600", "(US) Central Standard"},
    new string[] {"EAST", "+1000", "Eastern Australian Standard"},
    new string[] {"EDT", "-0400", "(US) Eastern Daylight"},
    new string[] {"EED", "+0300", "Eastern European Daylight"},
    new string[] {"EET", "+0200", "Eastern Europe"},
    new string[] {"EEST", "+0300", "Eastern Europe Summer"},
    new string[] {"EST", "-0500", "(US) Eastern Standard"},
    new string[] {"EASTERN", "-0500", "(US) Eastern Standard"},
    new string[] {"FST", "+0200", "French Summer"},
    new string[] {"FWT", "+0100", "French Winter"},
    new string[] {"GMT", "-0000", "Greenwich Mean"},
    new string[] {"GST", "+1000", "Guam Standard"},
    new string[] {"HDT", "-0900", "Hawaii Daylight"},
    new string[] {"HST", "-1000", "Hawaii Standard"},
    new string[] {"IDLE", "+1200", "Internation Date Line East"},
    new string[] {"IDLW", "-1200", "Internation Date Line West"},
    new string[] {"IST", "+0530", "Indian Standard"},
    new string[] {"IT", "+0330", "Iran"},
    new string[] {"JST", "+0900", "Japan Standard"},
    new string[] {"JT", "+0700", "Java"},
    new string[] {"MDT", "-0600", "(US) Mountain Daylight"},
    new string[] {"MED", "+0200", "Middle European Daylight"},
    new string[] {"MET", "+0100", "Middle European"},
    new string[] {"MEST", "+0200", "Middle European Summer"},
    new string[] {"MEWT", "+0100", "Middle European Winter"},
    new string[] {"MST", "-0700", "(US) Mountain Standard"},
    new string[] {"MOUNTAIN", "-0700", "(US) Mountain Standard"},
    new string[] {"MT", "+0800", "Moluccas"},
    new string[] {"NDT", "-0230", "Newfoundland Daylight"},
    new string[] {"NFT", "-0330", "Newfoundland"},
    new string[] {"NT", "-1100", "Nome"},
    new string[] {"NST", "+0630", "North Sumatra"},
    new string[] {"NZ", "+1100", "New Zealand "},
    new string[] {"NZST", "+1200", "New Zealand Standard"},
    new string[] {"NZDT", "+1300", "New Zealand Daylight "},
    new string[] {"NZT", "+1200", "New Zealand"},
    new string[] {"PDT", "-0700", "(US) Pacific Daylight"},
    new string[] {"PST", "-0800", "(US) Pacific Standard"},
    new string[] {"PACIFIC", "-0800", "(US) Pacific Standard"},
    new string[] {"ROK", "+0900", "Republic of Korea"},
    new string[] {"SAD", "+1000", "South Australia Daylight"},
    new string[] {"SAST", "+0900", "South Australia Standard"},
    new string[] {"SAT", "+0900", "South Australia Standard"},
    new string[] {"SDT", "+1000", "South Australia Daylight"},
    new string[] {"SST", "+0200", "Swedish Summer"},
    new string[] {"SWT", "+0100", "Swedish Winter"},
    new string[] {"USZ3", "+0400", "USSR Zone 3"},
    new string[] {"USZ4", "+0500", "USSR Zone 4"},
    new string[] {"USZ5", "+0600", "USSR Zone 5"},
    new string[] {"USZ6", "+0700", "USSR Zone 6"},
    new string[] {"UT", "-0000", "Universal Coordinated"},
    new string[] {"UTC", "-0000", "Universal Coordinated"},
    new string[] {"UZ10", "+1100", "USSR Zone 10"},
    new string[] {"WAT", "-0100", "West Africa"},
    new string[] {"WET", "-0000", "West European"},
    new string[] {"WST", "+0800", "West Australian Standard"},
    new string[] {"YDT", "-0800", "Yukon Daylight"},
    new string[] {"YST", "-0900", "Yukon Standard"},
    new string[] {"ZP4", "+0400", "USSR Zone 3"},
    new string[] {"ZP5", "+0500", "USSR Zone 4"},
    new string[] {"ZP6", "+0600", "USSR Zone 5"}
};

 

Then there is a static initializer of the class which creates a Hashtable for quick search.

private static Hashtable ZoneTable;

static Utils()
{
    ZoneTable = new Hashtable(50);

    foreach(string[] TimeZone in TimeZones)
    {
        ZoneTable.Add(TimeZone[0], TimeZone[1]);
    }
}

The actual conversion method is quite simple. First, try to parse the string without any change. This step can be skipped actually because all dates from an RSS Feed XML will contain the time zone name so this might be an overhead. If the parsing fails we replace the time zone name with the the actual offset.

public static DateTime ConvertWithTimezone(string StrDate)
{
    DateTime ConvertedDate;

    try
    {
        ConvertedDate = Convert.ToDateTime(StrDate);
        // just a plain date
        return ConvertedDate;
    }
    catch (FormatException fex)
    {
        // try finding a timezone in the date
        int TZstart = StrDate.LastIndexOf(" ");

        if (TZstart != -1)
        {
            string TZstr = StrDate.Substring(TZstart+1); // +1 to avoid the space character
            string TZvalue = ZoneTable[TZstr] as string;

            // its a timezone problem ...
            if (TZvalue != null)
            {
                // replace timezone name with actual hours (AEST = +1000)
                string NewDateStr = StrDate.Replace(TZstr, TZvalue);

                try
                {
                    ConvertedDate = Convert.ToDateTime(NewDateStr);

                    // success this time
                    return ConvertedDate;
                }
                catch (FormatException innerfex)
                {
                    // something else wrong, we dont know what to do
                    throw innerfex;
                }
            }
        }

        throw fex;
    }
}

Here we are. This is just like a wrapper on Convert.ToDateTime which modifies the date string before parsing it.

And have you noticed that the array of time zones is not complete. There are other time zones as well but I am using just the famous ones. The list of date times was taken from http://bytes.com/groups/net-c/214648-how-do-i-parse-date-w-time-zone.