From: 011netservice@gmail.com
Date: 2023-05-15
Subject: DateTime.txt

章節
	#### Round-trip Date and time values

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#### Round-trip Date and time values

The "O" or "o" format preserves time zone information. Round-trip means the formatted string can be parsed back to a date time value.

The "O" or "o" standard format specifier corresponds to the 
"yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffffffK" custom format string for DateTime values and to the 
"yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffffffzzz" custom format string for DateTimeOffset values.
大寫"O", Round-trip, "yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffffffK".
小寫"o", Round-trip, "yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffffffzzz", 例如: 2008-06-12T18:45:15.0000000-05:00

□ Round-trip a DateTime value
const string fileName = @".\DateFile.txt";

StreamWriter outFile = new StreamWriter(fileName);

// Save DateTime value.
// 本地時間
DateTime dateToSave = DateTime.SpecifyKind(new DateTime(2008, 6, 12, 18, 45, 15), DateTimeKind.Local);

string? dateString = dateToSave.ToString("o");
Console.WriteLine("Converted {0} ({1}) to {2}.",
                  dateToSave.ToString(),
                  dateToSave.Kind.ToString(),
                  dateString);
outFile.WriteLine(dateString);
Console.WriteLine("Wrote {0} to {1}.", dateString, fileName);
outFile.Close();

// Restore DateTime value.
DateTime restoredDate;

using StreamReader inFile = new StreamReader(fileName);
dateString = inFile.ReadLine();

if (dateString is not null)
{
    restoredDate = DateTime.Parse(dateString, null, DateTimeStyles.RoundtripKind);
    Console.WriteLine("Read {0} ({2}) from {1}.", restoredDate.ToString(),
                                                  fileName,
                                                  restoredDate.Kind.ToString());
}

// The example displays the following output:
//    Converted 6/12/2008 6:45:15 PM (Local) to 2008-06-12T18:45:15.0000000-05:00.
//    Wrote 2008-06-12T18:45:15.0000000-05:00 to .\DateFile.txt.
//    Read 6/12/2008 6:45:15 PM (Local) from .\DateFile.txt.



□ Round-trip a DateTimeOffset value
const string fileName = @".\DateOff.txt";

StreamWriter outFile = new StreamWriter(fileName);

// Save DateTime value.
DateTimeOffset dateToSave = new DateTimeOffset(2008, 6, 12, 18, 45, 15,
                                               new TimeSpan(7, 0, 0));
string? dateString = dateToSave.ToString("o");
Console.WriteLine("Converted {0} to {1}.", dateToSave.ToString(),
                  dateString);
outFile.WriteLine(dateString);
Console.WriteLine("Wrote {0} to {1}.", dateString, fileName);
outFile.Close();

// Restore DateTime value.
DateTimeOffset restoredDateOff;

using StreamReader inFile = new StreamReader(fileName);
dateString = inFile.ReadLine();

if (dateString is not null)
{
    restoredDateOff = DateTimeOffset.Parse(dateString, null,
                                           DateTimeStyles.RoundtripKind);
    Console.WriteLine("Read {0} from {1}.", restoredDateOff.ToString(), fileName);
}

// The example displays the following output:
//    Converted 6/12/2008 6:45:15 PM +07:00 to 2008-06-12T18:45:15.0000000+07:00.
//    Wrote 2008-06-12T18:45:15.0000000+07:00 to .\DateOff.txt.
//    Read 6/12/2008 6:45:15 PM +07:00 from .\DateOff.txt.