C# DateTime, is this method regional setting safe?

Question

I am using the following method to serialize a date as a string

private const string DateFormatString = "dd.MM.yyyy HH:mm:ss";
string LastsuccessfuldownloadDateTime = DateTime.Now.AddDays(-91).ToString(DateFormatString);

Is this the safest way to ensure that the string always gets serialized in this format?

Update on one server I have this running its completely getting the fields wrong.

Answer 1

I would use explicit invariant for serialization to avoid any unexpected gotchas. You may also want to think whether you need UTC or not; for example:

string LastsuccessfuldownloadDateTime = DateTime.UtcNow.AddDays(-91).ToString(
    DateFormatString, CultureInfo.InvariantCulture);