Parsing Culture-Invariant Floating-Point Numbers

I just came across this non-obvious behavior of double.TryParse:

We develop on German Windows, but the input field for float values should be intelligent to recognize both German (“,”) and international (“.”) notations for the decimal point.

Of course the functions to call to parse a string s into a double value are:

double f; string s = "double value as string";

double.TryParse(s, System.Globalization.NumberStyles.Float,
    System.Globalization.CultureInfo.InvariantCulture, out f)

double.TryParse(s, out f)

But the results were surprising

	InvariantCulture		default culture
string value	return (bool)	output (double)	return (bool)	output (double)
“100,03”	false		true	100.03
“100.03”	true	100.03	true	10003.0

My reasoning was, that if current (UI) culture could not parse the string, I let Invariant Culture try to parse it.

It turns out, however, that if the current culture simply removes all characters it does not recognize as valid input string for float numbers, and then parses the string, with the undesired result as seen above.

So the right way seems to try with invariant culture first, then use current culture:

double f;
double? Result;
if (double.TryParse(s, System.Globalization.NumberStyles.Float,
        System.Globalization.CultureInfo.InvariantCulture, out f))
    Result = f;
else if (double.TryParse(s, out f))
    Result = f;
else
    Result = null;