What is the C# equivalent of NaN or IsNumeric?

Question

What is the most efficient way of testing an input string whether it contains a numeric value (or conversely Not A Number)? I guess I can use Double.Parse or a regex (see below) but I was wondering if there is some built in way to do this, such as javascript's NaN() or IsNumeric() (was that VB, I can't remember?).

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

Answer 1

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 2

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.

update
secretwep brought up that the value "2345," will pass the above test as a number. However, if you need to ensure that all of the characters within the string are digits, then another approach should be taken.

example 1:

public Boolean IsNumber(String s) {   Boolean value = true;   foreach(Char c in s.ToCharArray()) {     value = value && Char.IsDigit(c);   }    return value; } 

or if you want to be a little more fancy

public Boolean IsNumber(String value) {   return value.All(Char.IsDigit); } 

update 2 ( from @stackonfire to deal with null or empty strings)

public Boolean IsNumber(String s) {      Boolean value = true;      if (s == String.Empty || s == null) {          value=false;      } else {          foreach(Char c in s.ToCharArray()) {              value = value && Char.IsDigit(c);          }      } return value;  }