C# equivalent of NaN or IsNumeric

Question

This seems like a fairly simple question, and I'm surprised not to have required it before.

What is the most efficient way of testing a string input is a numeric (or conversely Not A Number).

I guess I can do a Double.Parse or a regex (see below)

public static bool IsNumeric(this string value)
{
    return Regex.IsMatch(value, "^\\d+$");
}

but I was wondering if there was a implemented way to do it, such as javascript's NaN() or IsNumeric() (was that VB, I can't remember).

Answer 1

This doesn't have the regex overhead

double myNum = 0;
String testVar = "Not A Number";

if (Double.TryParse(testVar, out myNum)) {
  // it is a number
} else {
  // it is not a number
}

Incidentally, all of the standard data types, with the glaring exception of GUIDs, support TryParse.

Answer 2

VB has IsNumeric. You could reference Microsoft.VisualBasic.dll & use that function.

Answer 3

Yeah, IsNumeric is VB. Usually people use the TryParse() method, though it is a bit clunky. As you suggested, you can always write your own.

int i;
if (int.TryParse(string, out i))
{

}

Answer 4

I prefer something like this, it lets you decide what NumberStyle to test for.

    public static Boolean IsNumeric(String input, NumberStyles numberStyle)
    {
        Double temp;
        Boolean result = Double.TryParse(input, numberStyle, CultureInfo.CurrentCulture, out temp);
        return result;
    }

Answer 5

Try this for the sake of change.

static class StringExtensions
{
    public static bool IsNumeric(this string text)
    {
        return text.All(Char.IsNumber);
    }
}

Answer 6

In addition to the previous correct answers it is probably worth pointing out that "Not a Number" (NaN) in its general usage is not equivalent to a string that cannot be evaluated as a numeric value. NaN is usually understood as a numeric value used to represent the result of an "impossible" calculation - where the result is undefined. In this respect I would say the Javascript usage is slightly misleading. In C# NaN is defined as a property of the single and double numeric types and is used to refer explicitly to the result of diving zero by zero. Other languages use it to represent different "impossible" values.

Answer 7

public static bool IsNumeric(string anyString) { if (anyString == null) { anyString = ""; }

        if (anyString.Length > 0)
        {
            double dummyOut = new double();
            System.Globalization.CultureInfo cultureInfo = new System.Globalization.CultureInfo("en-US", true);
            return Double.TryParse(anyString, System.Globalization.NumberStyles.Any, cultureInfo.NumberFormat, out dummyOut);
        }
        else
        {
            return false;
        }
    }

Answer 8

maybe this is a C# 3 feature, but double.NaN;