String contains only a given set of characters

Question

I need to know if a given string is a valid DateTime format string because the string may represent other things. I tried DateTime.ParseExact(somedate.ToString(format), format)

Answer 1

There's a new project, NLib, which can do this much faster:

if (input.IndexOfNotAny(new char[] { 'y', 'm', 'd', 's', 'h' }, StringComparison.OrdinalIgnoreCase) < 0)
{
    // Valid
}