How do I format a DateTime to ISO 8601 in C#?

To format a DateTime object to ISO 8601 format in C#, you can use the built-in formatting capabilities of the DateTime struct along with a specific format string. ISO 8601 specifies a standard way to represent dates and times, which is crucial for data interchange and consistency.

Here's how you can achieve this:

1. Using the "O" or "o" Standard Format Specifier:

- The "O" or "o" standard format specifier is designed to produce an ISO 8601 compliant string. It includes the date, time, and timezone information.

2. Example Code:

using System;

public class Example
{
  public static void Main(string[] args)
  {
    DateTime now = DateTime.Now;
    string iso8601String = now.ToString("o"); // or now.ToString("O");
    Console.WriteLine($"Original DateTime: {now}");
    Console.WriteLine($"ISO 8601 Formatted DateTime: {iso8601String}");
  }
}

3. Explanation:

- DateTime.Now gets the current date and time.

- now.ToString("o") or now.ToString("O") formats the DateTime object into an ISO 8601 string. The output will look something like 2024-07-26T14:30:45.1234567+00:00, including the timezone offset.

4. Handling UTC Time:

- If you need to represent the time in UTC, use DateTime.UtcNow instead of DateTime.Now. The resulting ISO 8601 string will have a "Z" at the end, indicating UTC time.

DateTime utcNow = DateTime.UtcNow;
string iso8601UtcString = utcNow.ToString("o");
Console.WriteLine($"UTC ISO 8601 Formatted DateTime: {iso8601UtcString}");

5. Custom Formatting (Less Common):

- While the "o" or "O" specifier is recommended, you can also use a custom format string if you need a specific variation of ISO 8601. For example, "yyyy-MM-ddTHH:mm:ssZ" for a basic ISO 8601 format without milliseconds.

By using the "o" or "O" standard format specifier, you can easily and reliably format your DateTime objects to ISO 8601 in C#, ensuring compatibility and consistency across different systems and applications.

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