parsing - 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

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; 
}