DateTime to String with Custom Formatting

When formatting DateTime to a string, the format specifier provides access to the parts of the date and time we want to express as a string. E.g.

DateTime.UtcNow.ToString("yyyy-MM-dd HH:mm:ss.fff")

will produce something like 2024-11-03 12:34:56.789. But, you must be extra careful with the time separator :. It's not always the same for all cultures, and if an explicit culture is not specified, the default local culture might surprise you. Let's see an example.

Let's say the code is running on a machine set up with Finish culture.

DateTime.UtcNow.ToString("yyyy-MM-dd HH:mm:ss.fff", new CultureInfo("fi-FI")).Dump();

The same code snippet used earlier produces an entirely different result, 2024-11-03 12.34.56.789. But how is that possible? That's because the : custom format specifier is culture-specific. The separator character must be specified within a literal string delimiter to change the time separator for a particular date and time string.

DateTime.UtcNow.ToString("yyyy-MM-dd HH':'mm':'ss.fff")

Or escaped.

DateTime.UtcNow.ToString("yyyy-MM-dd HH\\:mm\\:ss.fff")

Escaping would be required to avoid surprises if date formatting yyyy/MM/dd is needed. Find more about date and time separator specifiers on MSDN.