What does IFormatProvider do?

Question

I was playing around with the Datetime.ParseExact method, and it wants an IFormatProvider...

It works inputting null, but what exactly does it do?

Answer 1

In adition to Ian Boyd's answer:

Also CultureInfo implements this interface and can be used in your case. So you could parse a French date string for example; you could use

var ci = new CultureInfo("fr-FR");
DateTime dt = DateTime.ParseExact(yourDateInputString, yourFormatString, ci);